Okay I need to chime in here.
Besides being an N97 owner since July, I have owned two (2) N800's for the last few years, so I speak from the perspective of the Maemo 4 OS on a touchscreen platform.
I expect the N900 to behave pretty much as the N800/N810 does with respect to performance. With the Linux Maemo platform and interface you can juggle a lot of tasks at once.
BUT you probably don't really want to...mainly because the battery life doesn't come close to the N97's performance.
I used my N800's to replace a laptop for internet browser and note taking. If you do much WiFi or video watching you can expect about 3 hours worth of use before the battery gives you up. If you don't close all of your applications before the battery finally runs out you risk losing any data if not already saved.
As far as being stable, I have had to reboot my N800's many times when a program was misbehaving, locking the N800 up or sometimes it would even spontaneously reboot on its own.
As I have mentioned before...the problem with the open-source platform like the N800 is that the software is worth what you pay for it. Someone would typically get interested in "porting" a Linux application to the N800/N810 and would do about an 80% job on the port. Where the applications really suffered was on the "Hildon-izing of the interface". That is, the screen is only so big and a lot of the software doesn't automatically resize, add scroll bars, etc. so often you are left with combo boxes off the screen, overlapping or unreadable text or unselectable check boxes/targets as they computationally overlap on the interface. If you don't believe me, check out the porting of Gnumeric (spreadsheet application).
Now granted there are some good programs out there, but few of the authors consider them a "labor of love" so that they are ready, willing and able to help troubleshoot, debug, recompile and repackage the program for updates.
There are a lot of lost-and-forlorn applications waiting for someone to finally clean them up.
It's like being a perpetual beta tester.
And to make things work you often have to consult the user forums and hand-enter patches, fixes, tweaks at the root level at a Linux prompt after gaining root. If you are new to Linux, get ready for some culture shock.
Unless the N900 comes with some rock-solid stable apps right out-of-the-box, I see it becoming only a hacker platform (did I mention that there's a "Hackers Edition" of the Maemo OS available?) or a techno-geek status symbol.
What is sad to see is the countless hours spent by some of these programmers just to get games from the C64, Nintendo, Sega, etc. running on the platform. If only that effort were spent getting some of the work-related applications running better.
I won't be one of the ones buying an N900.
