My impressions after a week of usage, these are only points of that can be improved.
The list of what i like is just to long...

The fist few days the battery did go down quickly yes.
But currently now i am more in my normal usage, it can handle a full day pretty easy.
But i do think that there are things that drains the battery (like large inbox which is fixed for the next firmware if i am not mis informed)

First i miss voice dialing when i am in my car, this for example is a much higher prio then for example MMS, if it was me dont bother implementing that at all
What the use of MMS is besides paying a lot of money to the operators i don't know.

What i do find strange is that the DateFormat is depended on language not region setting. How come?
That is a region setting, not a language setting. But it should be completely configurable if you ask me. give me an option to set a date format completely free of language or region settings
I guess a fixed list could be possible if there are enough choices..
But currently i am ok with the UK language and the Dutch region (i don't want dutch language on my phone or on any electronic device that i have)

What i do notice is that not all clicks are really coming through. But this is not the hardware screen itself as far as i can see. Because the click is somehow coming through because i see selection, i hear the click sound,
the link being highlighted but the link in the browser (where i see it the most) is not really clicked. It seems to me that the balance between is it scroll or really a click is not completely configured right.
I think there is some area of improvements here.

Calendar
Birthday Alarm. Only day before? i want same day around 10..
I want to have default alarms on all my Birthday entries
Birthday: only in widget when within 2 weeks, i always want to see them..
Default view open view, remember last view i was on. I almost always want to be in month view.
New event, remember last used calendar, now it always goes back to the default N900 calendar.
better google exchange support (works a bit but not completely)

Music player
Sort by album artist, i really mis this option, now i always do artist but then it is garbage and with albums it is a random mess...
Album art? I cant figure out what it needs for image and what the name it should have. Some do have album art but most don't.


Email
imap idle support, this is really quite annoying that i don't have this. On my E90 with profimail i had perfect push email.. The current way of polling as much as possible drains battery.
many times the email doesn't open when clicking on it in the taskmanager.
when it does open through taskmanager that email cant be deleted you have to go through the inbox (the trashcan is disabled)
Deleting an email goes to the next email, i want to go to the list(inbox)
inbox is slow, but this is already fixed for the next firmware, i believe it was constant sorting of all the mail. the fix only does the top 200 or something.
i also hope that this fix is the same when deleting emails and so on. the cpu usage does spike then, which i dont always expect to happen.

Web
bookmarks view, if you start typing there it should filter/search the bookmarks (awesomebar of FF)
When i am in zoomed in mode like double tab and i click a link the browser should first zoom out before repainting the next page now it is a 2 step first if see a portion in the same zoom level as i was in and then it zooms out
weird thing is that this is not always the case on every website, but it is on my-symbian maemo forums.
The browser is 1 of the biggest cpu hog component (together the email client and large inbox currently). I really hope that this can be optimized further on


Contacts
skype birthdays are not mapped to contact/calendar birthdays

phone app
If i have a number that is not in the contacts but is in the call list, i have an option to sms. But a know contact/telephone number that is in the call list i suddenly don't have the option to sms it. I really have to open the contact card and then press sms.

IM
Sometimes i get a message but the contacts/im window isn't or doesn't open, only see it in incoming message widget, i guess this is the same thing with emails that don't open when pressed. I then have to go through the conversations app to really reply to it.
Incoming message widget should have an option to open the im window to reply on it
Incoming message widget does show last message fist this should be reversed else i read threads to the same person in reverse order thats confusing
No attachment support, it would be nice if a skype person sends me a file that i get to option to save it.
Incoming im seems to take a lot of cpu sometimes, i do have a large history maybe the same problem with sorting it like the email client had? Even when the im window is in the background i see the floating popup the cpu spikes and its very hard to open the im window fast, it really seems that displaying the history is taking a lot of time.
it would be nice if talk/skype/msn had 1 combined history

Maps:
This is really the worst part in my eyes..
On Sunday when i followed a route, the map was constantly jumping around, it seems to me that it constantly thought that i was on a different location. But when i turned of track me and clicked my self the Red button of my current position it always had it right..
The next day i tried it again but didn't have that constantly jumping around problem. But the map is lagging a bit behind. I was already stopped at a point and then the maps app did 3 more jumps before it was on the place where i was now.
Also when stopping it changes rotation sometimes. It shouldn't do that. It should only change rotation when i am moving again.
The general search box is nice, but we should really have a address search box including typeahead or how TomTom it does with a keyboard that only shows the possibilities that still can be pressed.
In general it missed a lot of features Maps 3.0 on Symbian already has
I hope they improve the maps a lot and that they add voice navigation and no it doesn't have to be free. If the program works like Maps 3.0 i have no problem paying for it.

Stability:

N900 did reboot now on its own 2 or 3 times in 8 days and one time had to take the battery out my self, are there any logs to see why?

What happens to me more often is that it looses contact with the sim card. i have to type my pin code for my sim card now and then because it did loose it.
I still have to look into this a bit more and see if it is not just my sim card or a problem with the connections.

what happened to me yesterday was that i got a out of mem error and it told me to close all applications before i could start another application.
It was a pity that i didn't have the Terminal open at that time because closing down all applications didn't improve it. I had to reboot myself
Weird thing is that the load applet didn't show any big memory use i think only 2 bars.. So i think some other type of handles (file handles) run out of something..
I hope if this happens to me again that i have a terminal window open and i can check these things. Any pointers what i should check then?


This is really quite a list of things that could be better or should be better, but don't think i don't like it.
I love the device, it is finally a replacement of the E90 but it could need some fine tuning.
And i know that i am an early adopter in that area so most issues don't bother me to much.