I have some concerns about the battery life here too. My current phone is the i8910, which spec wise is very similar, but it has a 3.7 AMOLED screen (lower energy consumption) and a 1500mA battery. Even with a less power-consuming screen and better battery I have to curtail my use a little to get through a day.

A typical day is GPS tracking via sportstracker for around an hour as I cycle to and from work, about a 1-1.5hours streaming from lastfm, half hour browsing, an hour miscellaneous screen-on use (gaming/document viewing/GPS use/Fring etc/taking pictures or video/ watching video), continuous push email, and the usual telephony stuff.

As things stand I doubt the N900 will be up to my current usage, let alone improving things so that I don't need to cut back on browsing/gaming in order to get through a day...