jaem's analysis is really really good, and matches mine fairly well. Some additional points:

* I have no problem with the screen size on my n900 as compared to my n810, but then again, people keep telling me I have freakishly effective eyes that can see things no human being has any business seeing.
* I never tried playing games with the D-pad (I can't get effective gameplay unless it's an actual game controller layout). In this respect my n900 is actually better than the n810, since it's much easier to hook up an actual game controller (I have sixaxis controller support installed).
* I also thought USB OTG - which the n810 has, but the n900 doesn't - was really cute, but since it only worked for low power devices I ended up pretty much never using it and I have yet to miss it at all.
* Automatic portrait mode in the web browser ABSOLUTELY ROCKS and makes up for a lot of my foibles with this thing. Similarly, I used to have some interest in alternative web browsers on the n810 in the hope that it'd improve the user experience a bit - this need has lessened for me on the n900 (although that's entirely subjective; YMMV).
* I also really really miss the n810's kickstand, although I occasionally get by with having one finger through the one on the n900. It sorta works, although it's not as comfortable and not as effective. If someone out there could come up with an aftermarket battery door with a full-width kickstand (without screwing up the camera cover and MicroSD card setup like Mugen Power did with their battery door), I would love them forever.

I honestly haven't used my n810 since I got the n900 - except to occasionally grab a file or two to try some compatibility hacks (mostly for the HAVA mobile player, which doesn't work on the n900 ).

As a book reader, I often find myself using the N900 in preference to the Kindle, which is equally in reach here. The N810 is even better as a book reader, but the N900 can do so much more so much faster. The browser alone is incredible on the N900. Witter is a great Twitter client for the N900. And lots of the programs that were so good on the N810 are faster and nicer on the N900.

I love my N810 because of it's openness not only with software but the host mode USB. When I found that Bluetooth keyboard software support was poor on the N810 I was able to use a small USB keyboard to draft blog posts and chapters of a book. The USB also allowed me to easily transfer files to and from USB memory sticks which are universally read by any PC. Lastly the USB allowed me to access pictures from the SD card in my camera. The N900 is more phone and less computer. I bought the N810 in part because it wasn't a cell phone burdened with carrier controls and limits on access. One has to wonder is the lack of USB was a marketing ploy to differentiate netbooks from the N900. I can't see a technical reason for eliminating USB since that connector is becoming the standard charging systems on phones.

I agree with most of your post, but I'm a bit puzzled as to what you think has been "limited" or "controlled" by the carriers. If some carriers have done stupid things with the firmware (I don't know), then I agree that that stinks, but it's also par for the course, and the N900 is available unlocked and untampered with in any case.
As for USB host, no, it wasn't a marketing ploy. I never did get clear exactly what happened with that, but my understanding was that something fell through late in the design stage, and that caused problems with certification... or something. There's a huge forum thread or two on it if you care to read them - it became rather convoluted. -shrug-

Things I liked about N810 was slim and very compact built, bigger screen and of course the awesome kick-stand. However, N900 outbit N810 in many aspects other than the ones I just mentioned about N810 and the usb OTG mode though not a big deal.
- N900 has less keys but N810 has very stiff keys and hard to press whereas its very smooth in N900.
- Of course the hardware and the 3D support in N900
- It is good to browse in N810 but though small screen, support for kinetic scrolling, auto-rotation, gestures for zooming and history etc etc.. I know you are enjoying the browsing in N810 now and so was I but trust me after the browsing in N900 it will change a lot of your thinkings BTW, zooming in N810 was a pain and so ugly.
- Media player just amazes me (I know there are few things ppl complaining about) but whatever movie I have in my comp or hard drive or anywhere, I just copy them to my N900 and its good to go instead its more crispier and ultra clear..
- Now you are writing some code, hacking, note taking or whatever, you receive the call or make one from the same freaking device, isn't that totally awesome
- Inbuilt IMs now coming with video support(ya N810 could also do this)
- What da.. just slide the camera cover open and take widescreen (3.5 MP) or normal 5 MP photos or just change the option and take what used to be the second largest resolution video in the mobile world but i thing now sony erricson or some company has introduced 854x480 res video as N900 takes 848x480.

Sorry, I got tired. Stopping now. Decission is all yours.

By Carrier control I mean things like literally forcing you to buy their over priced ringtones or placing limits on the use of VOIP. They remove from manufacturer docs any information that would enabled to create your own ringtones or load your own music. There UI's only provide a way to purchase from them. Granted my experience in this area is limited the most basic of smart phones and I've no personal experience with the N900 -- only what I've read about it. I'm sure they came up with an appropriate excuse for not including USB. Eliminating EMI is a black art but very doable. Even the radius of a trace turn on a PC board has an impact. Class B has been achieved on uncased circuit boards with fast microprocessors and a number of physical high speed data ports -- my engineering team did it.

I can't speak for documentation, but the N900 is pretty darn Open - to my knowledge, nothing is being fiddled with on the phone (or at least, nothing that can't be undone - I've never used a carrier-sold N900). As for ringtones and music, well, heck - the N900 is a computer, so why wouldn't you be able to load whatever you want on it? The carriers couldn't lock that down without locking down the whole phone, and let me assure you, they aren't doing that. Nokia's attitude, at any rate, seems to be "it's your phone, go nuts!", which is exactly what it should be. As for VoIP, that's a network thing, and while it may be annoying, if you're using their network, you're subject to their rules. You can run whatever you want on the N900 itself, but if the carrier decides that they don't like a service, they do technically have the right to block it on their network, much as it bothers me. Of course, since it's a computer, there may be all sorts of fun tunneling and such that you can do to get around that if that's the case.
So no, Nokia has not "sold out" to the carriers.
I hope that clears things up.

n900 - smaller screen (I preferred the larger one)
n900 - great camera
n900 - better faster browser for reading (hard to go back)
n900 - opens pdfs faster
n900 - usb charging - and don't have to worry about charging 2 devices (cell and table)
n900 - awesome integration of chat and skype
n900 - videos play a bit faster (some larger .avi files my n800 would choke)
n900 - Meego ready

After using the N900 for 120 days, I have changed my mind on the N900 screen. Now I think the N900 screen is "small", no longer "too small". Why is that? Because of the super smooth kinetics scrolling. With the smooth kinetic scrollings, it is more than adequate to make up the small physical screen difference between N900 and N810.

Back to CyberCat's question:
wrt N900:
80% games - N900 has to be better, with the addition of the g sensitivity
15% GPS/Maps - GPS locking is better; ovi maps, if you put your mind to it, like learn how to use it, it is almost comparable to maemo maps. ovi maps allow one to dl the whole world maps on your N900 and the POI is very 'rich' (The whole world map in your tablet, feeling and use is quite different ), maemo maps is very functioning, like saving the route and more, but you need to plan for it before the trip and carefully dl the part of the map.......anyway, one can write a book about the difference. For me, ovi maps at the current status is about as good as maemo maps.

3% browsing: There is no comparison; with the kinetic scrolling, smooth browser, no crash on web browsing over 120 days . Only Tear can barely match up with the N900 browser

2% quick note: never use, dont know

WorldTV99 for media streaming, N900 is almost there, the built-in media player is much better than the built-in one on the N810. I am using my N900 as my major news catchup nowaday, rarely turn on my 27" any more.

From N810 migrate to N900, one point nobody mention is the finger friendliness. On the N810, I rarely use finger, I always wip out my stylus before anything else, as more often than not, I encounter areas are way too small for my finger. Cannot believe a die-hard stylus user, has now convert to finger use on the N900. The maemo5 OS does encourage finger friendliess on its programming, like recommendation of font size and distance between lines etc. Today, I rarely wip out my stylus on my N900.

With my assessment of your needs, you are asked to jump onto the N900 bandwagon, NOW


bun

For that particular use pattern the N900 is better. The only exception might be the 2% note taking, due to the differences in input methods and hardware keyboard layouts. For the GPS part I found Sygic mobile maps to be vastly superior to ovi maps/wayfinder/navicore.