I've had horrible battery life for the first 2 weeks of owning the device, but everything just changed.
I used to get about 10-12 hours max always connected, without much usage.
My battery life has increased considerably **EdIT**
I'm not completely sure as to what did the trick.
**EDIT** I Believe the cause of my battery life increase may have been due to a combination of better reception, and maybe just getting past those first few charge cycles to get the battery to its full capacity.

What I've done before this happened is disabled the touch search widget, and the media player widget.
After doing this I noticed that the 25% battery I had left suddendly seemed to last forever.( Draining about 1-2 % per hour on idle while connected to 2.5G and a wifi connection.)

The next charge after that had the following results:
When in online mode I was always connected to a wifi, except when driving. I had email checking every hour, omweather every 4, and msn haze plugin always on always connected.

~ $ lshal | grep percen;date
battery.charge_level.percentage = 97 (0x61) (int)
Fri Dec 18 01:43:05 GMT+8 2009 removed from charger as soon as turned green.
~ $ lshal | grep percen;date
battery.charge_level.percentage = 92 (0x5c) (int)
Fri Dec 18 02:59:17 GMT+8 2009 after a little browsing before bed
~ $ lshal | grep percen;date
battery.charge_level.percentage = 87 (0x57) (int)
Fri Dec 18 13:23:30 GMT+8 2009 kept n900 in offline mode overnight. Set back to online.
~ $ lshal | grep percen;date
battery.charge_level.percentage = 83 (0x53) (int)
Fri Dec 18 14:28:03 GMT+8 2009 10min chatting, 10 min talk, updated 2 apps. Uninstalled ssh-server.
~ $ lshal | grep percen;date
battery.charge_level.percentage = 68 (0x44) (int)
Fri Dec 18 17:02:00 GMT+8 2009 about 35 mins of talk, a couple of texts.
~ $ lshal | grep percen;date
battery.charge_level.percentage = 65 (0x41) (int)
Fri Dec 18 18:00:18 GMT+8 2009 just checking email
~ $ lshal | grep percen;date
battery.charge_level.percentage = 62 (0x3e) (int)
Fri Dec 18 18:28:28 GMT+8 2009 checking battery and email
~ $ lshal | grep percen;date
battery.charge_level.percentage = 61 (0x3d) (int)
Fri Dec 18 19:55:24 GMT+8 2009 just checking battery.
~ $ lshal | grep percen;date
battery.charge_level.percentage = 60 (0x3c) (int)
Fri Dec 18 20:34:10 GMT+8 2009 just checking battery.
~ $ lshal | grep percen;date
battery.charge_level.percentage = 57 (0x39) (int)
Fri Dec 18 22:05:29 GMT+8 2009 checking battery, messages
~ $ lshal | grep percen;date
battery.charge_level.percentage = 51 (0x33) (int)
Fri Dec 18 22:57:02 GMT+8 2009 15 mins of playing an online game.
~ $ lshal | grep percen;date
battery.charge_level.percentage = 35 (0x23) (int)
Sat Dec 19 02:03:10 GMT+8 2009 listened to just over 3 hours of mp3s on shuffle.
~ $ lshal | grep percen;date
battery.charge_level.percentage = 22 (0x16) (int)
Sat Dec 19 04:42:20 GMT+8 2009 on drive home, listened to 10 mins of music with fm transmitter. Checked messages periodically 45 min drive.

And finally just wrote this whole post and browsed tmo for the past~50 mins, and here is the final battery read.
~ $ lshal | grep percen;date
battery.charge_level.percentage = 13 (0xd) (int)
Sat Dec 19 05:25:36 GMT+8 2009

overal very satisfied with the increase in battery! Not sure what exactly made the difference. I'll test those widgets one by one on my next charges.