Thanks for posting this.
I today got my N900 and i am about to get 6 hours as from what i can say about the status right now. Maybe less.
I have had 3G on half of the time at least. No wifi, though a 5 hr bluetooth session of data sending(cant get a normal cable transfer session with ovi suite working right now) and half of the time browsing and personalizing. It looks messy but i hope with 3G, BT and wifi off in standby, with no widgets on and all services updating almost never, brightness on 2(for when the screen is on) i will get more than 15 hrs.
I am very certain it has to be able to do that.