I don't think it will be worse than my e90 battery life, wich i charge every night until morning(7-8am) and after browsing some web, listen to music, play some games (that is about 2pm) the battery is at the last line - so i charge the phone about twice per day. And so i am kind of used to have a crap battery, but if n900 could resist from 8am to 10pm without a charge it is perfect.
Windows phone 7 is a joke - a big mistake from microsoft- instead of improving and innovating windows mobile, they start all over from scratch and with the left foot, i mean come on this os doesen't stand a chance even in front of my old s60v3 os 9.2 e90 look at the limitations: Windows Phone 7 OS LIMITATIONS: No system-wide file manager No videocalling Limited third-party apps availability No Bluetooth file transfers No USB mass storage mode No multitasking No copy/paste Too dependent on Zune software for computer file management and syncing No music player equalisers No Flash or Silverlight support in the web browser No sign of free Bing maps Navigation so far No DivX/XviD video support No internet tethering support New ringtones available only through the Marketplace Swapping memory card requires hard reset; cards not readable by computer