I've got my N900 10 days ago.

The battery lasts between 12-24 hours. 12 hours is with heavy usage:

- 2-3 hours surfing
- email check every 5 mins
- wifi scan every 10 mins
- foreca widget (1h interval checks), load applet
- 1h internet radio
- 10 min phone calls (several calls)
- 4-8 photos with flash
- 2-3 mins video recording
- 10h wifi connection
- 2h 3G connection

Usually I am doing about 16-20 hours with a fully charged battery and I am pretty happy with it. After reading this thread I've done some tweaks which will improve battery usage. I think this will help a little more.

With some tweaks and light usage one should be able to do 30+ hours on a full charge.

For me 18 hours with moderate usage is very acceptable. Anything more is a bonus