I can offer insight from a Clie user perspective...I have an nx73v.

first no way you can completely replace the PIM functionality of your Clie yet on an N8x0.

Most of your existing favorite PalmOS apps are not ever going to be out for the N8x0 or will never have counterparts during the lifespan of the device. Though there is a chance that you can use the Garnet VM (GVM) for Nokia N8x0 tablets to run a fair number of them. HandyShopper is said to run well but I have yet to try it out.

I am also finding that the developers for Maemo apps are not remotely interested in anything beyond media related applications. A sign of the times I guess but I expected more development in the area of desktop apps like word processing, database management or just client apps. PIM stuff is in the devstream as are a small few apps of other sorts, but the majority seem oriented toward entertainment/multi-media. What I am saying is have realistic expectations of what is out there for Maemo...not much when compared to PalmOS apps.

But many can currently run via the GVM, not a perfect solution but could hold you over until better options come along.

Recently (yesterday actually) there was a post about Google Gears being close to running on the Nokia Maemo platform. Apparently there is an Alpha version out now and it's pretty slick. Basically they explained to me it allows offline use of online apps like Google Docs and RememberTheMilk (really cool app I never knew existed, sort of like HandyShopper with PIM rolled into one...I think after my 30mins looking at it...) So maybe what I am looking for in the device will be covered via Google Gears. I might even work on converting my personal SQL front end pages into a single app that will function under GG...not sure if it would go that far but it's on my ever expanding To-Do list.

Also, I am not sure of the build quality of the TH55 but the nx73v is built like a tank with a great metal case and, well, just very well thought out. I can say the build quality of the N800 is nowhere near as good as the nx73v, as in they are not even in the same league. That is not to say the quality of the N800 is not good. It's adequate but will certainly require far more gentle handling to survive as long as my beloved NX.

The ergonomics are well, different. On the NX I am especially addicted to the thumb accessible thumb wheel. But I have begun to adapt to the quite different ergonomics on the N800 and it's OK and just different. I do find it's impossible for me to operate the N800 one-handed like I can the NX. But then again few devices ever have matched that part of the NX series design.

One last issue that is significant to me is you can turn off the backlight on the Clie's and use them quite easily in direct sunlight, in fact the more sun the better, this is not possible on the N800. But the N810 does have a trans-reflective display that actually uses ambient light to improve the display, especially in the sun. So if you use it outside you might need to weigh the importance of the much greater memory capacity of the N800 vs. the far superior display in sunlight or rooms with a lot of windows. It is a factor that would be easiest to determine if you could compare the devices side-by-side.

What is BETTER on the N800 is, well, it's current and have a great core following. Despite the somewhat poor build quality for a mobile device it's solid enough. And it's better then most other mobile devices I looked into.

Obviously storage capacity is much greater on either of the N8x0 devices. But, the only capacity issues I have on the Clie is for video's or audiobooks.

Audio & video ability on the Nokia's is also much better. They can even play streaming video if properly formatted for the tablets (that really matters.) Audio streams play perfectly.

Battery life is pretty much a wash and equal between my NX and my N800. Also I have a hacked driver for my Wifi card for the NX so it has the same wifi as the N800.

Hands down the best difference is the browser and internet access portion of things. The Clie's don't even come close to the NIT's. Under OS2008 pretty much every site I have visited renders correctly. One thing the browser cannot make up for is a poorly designed web page/site. If the site uses teeeeeny fonts w/o the ability to change the size you only option will be to zoom the page. This leads to lateral scrolling which drives me batty. Still at least the page renders whereas it would either not load or look so awful in Netfront it's not worth the effort.

The N8x0 supports VoIP as well as Skype (which is actually not VoIP). No chance for that on the NX for me, not sure how well the TH55 might work there but I seem to recall it's a no-go for calls.

I like FBReader on the N800...ever nice app. Works differently than eReader but I find it an excellent application which offers excellent control over on-screen formatting. Only caveat is no DRM books. And I doubt that will ever change. But like you say one can find a LOT of content free at Baen, Project Gutenberg, and FeedBooks (more reliable editions of PG books). Also over on http://www.mobileread.com/forums/ebooks.php there is a forum where several users have done yeoman duty to create AMAZING editions of just oodles of books from PG in all manner of formats.

Ignoring the outdoor viewing issue on the N800, the display on the N8x0 series is a HUGE improvement, even over the great quality on the nx73v's 320x480 HiRes display.

Overall I love my N800 and am not sorry to own it in any way. I knew it was a niche device as well as a very immature product. But developers are improving it's usefulness. So, perhaps before I die I will get the same info management use from the thing. In the mean time I find I must carry both devices most times as I really do not like using the GVM at all as it is small, and, well, Bufugly plus Access would pull the plug on it tomorrow...I mean we PalmOS users all know how poorly every PalmOS oriented company has treated loyal customers over the past 5-years. Funny the devices are still so in demand. Heck, my nx73v is 4-yrs old and I could get $150+ on eBay tomorrow if I wanted to sell it...

Sorry for the long winded response...take it for what it is, just my opinion. I am not expert in any of this at all but do value the information management aspect of the PalmOS devices. And Sony Clie's were the best made of the lot of PalmOS devices just it was Sony who considers customers mushrooms to be kept in the dark and have, well, you know what shoveled over the top of them.

Hunt around here and you will see threads about PIM packages and also over on the Maemo site you will see a few in their early stages. Now that I am aware of Google Gears for the N8x0 with OS2008 I am more hopeful of better functionality from the N800 I have. In the mean time it's a fun way to watch video on the go, browse the web on the road and also just have good time with a new device.