I've been having to force close a number of applications on my n900 lately, and I can't figure out what would've changed in my system since this started. Typically I have to force close (i.e. apps not responding) conversations, calendar, web, and hildon desktop a few times a day. I have not added any apps recently and the only item that was changed was removal of theme customizer a few weeks ago.

Any ideas or suggestions?

time to re-flash?

Download conky and see what is taking up most of your ram or cpu. Uninstall that app or avoid that function.

If that doesn't fix it then download swappalubenogui from app manager (spelling might be wrong). This should make your phone a lot more smoother, I use this and phone runs perfectly.

You may also want to overclock, 850 is stable and more than enough.

If all of the above fail then just reflash.