I've had my N900 for about 3 weeks now.
I've dowloaded a number of apps, themes and widgets from both main and testing/devel.
Some I've kept and some I've uninstalled after trying and not being happy with the impact they've had on the OS or performance (just like my linux PC and Laptop)
The only real grief I've had is the screen lock issue making for some fiddling to end calls occasionally.
Is it possible that we (as in consumers) are expecting too much from "bleeding edge" devices when it comes to stability and function?
My list below, of previous phones:
SE P800/P910 - both with their inherent "idiosynchrosies"
SE W950 slow and laggy, but improved after 2 x fw updates
Palm treo 650 crashed frequently and killed the battery until a fw update
HTC Touch Diamond - Microsloth Mobile - say no more
SE W960i - slow and buggy until reflashed with WWE FW and then still slow.....
Nokia 5800 - all sorts of problems which took 4 x FW updates to get sorted
SE Satio - Just like the 5800 but with a 12mp camera. only one update so far but still not great....
N900......

I've got used to new devices with issues. and my expectations of the N900 are no different.
Hit some other brand forums and you'll see everyone else is complaining about bugs and issues in their respective devices/platforms as well.
the need for manufacturers to be 1st with the latest gear on the market is the driver behind the delivery of "unfinished" products.
you only need to see all the whinging about PR 1.2 on this forum to see the sort of pressure manufacturers are under to deliver. It's the " I want it now" generation at it's finest.
for me. I'll put up with the bugs and wait patiently for the next FW release.....

then again when it comes to updates, there's nothing like owning a SE smartphone to teach one patience.

just my 2 bob's worth