The one issue with battery life is there's a glitch in one of the built-in applications - "hildon-desktop". If certain conditions happen, the thing is -always- running at a low level, eating battery life at a high rate.
Fortunately, there's a patched version of it that fixes the problem entirely, and can be installed easily in a minute or so. Once that's installed, battery life is always good and tends to be predictable.

The N900's a great machine, but -- as people have noted -- some of the software has glitches and or missing functionality(But what -doesn't-?). Being very open, however - There are fixes, updates and 3rd-party apps which solve all those problems.