So I got my Mugen power 2400 mAh battery some days ago.
and this is what i've been seening so far.

First time i put the battery in, i charged it up to 97% (my battery widget never shows 100%)

February 3rd: I woke up at 06:00 at 97% battery, left for work, got to work at 08:00 and i had lost maybe 2 % battery(with some sms and quick talk.maemo.org surf)
Did some minor chatting on facebook chat on WIFI, left work with 89% battery, got home and did some modding and desktop changes on the n900, installs ect. Went to bed with 57% battery. (was on wifi for some hours while modding)

February 4th: Woke up at 06:00 with...yes... 57% , same as i went to bed with. (didnt charge overnight). By the time i got to work i had 56%, did some wifi surfing, sms, and some calls at work. left work at 14:00 with 44% battery. Got on the buss and did some 3g surfing on talk.maemo.org, while connected to the facebook chat. At the gym 1 hour after work (beeing on 3g and facebook chat, and sms 1 whole our after work). At the gym i had 39% battery life. switched of 3g and facebook chat. and left the phone in my locker. after 2 hours at the gym i was at 38% battery. went on the buss home and did some 3g , facebook chat, facebookphotouploader, and some minor surfing for 30 mins on the buss. got home with 30% battery at 17:45(-+). turned 3g and shut down the facebook chat. Now at 18:15 i checked my battery , and it went from 30% to 34%. and the phone was just been idle at the table.

So my conclusion is, the mugen battery fits me perfectly. On the stock battery it would not last 1 day , but now i can get 2 days with daily use of the phone. Though i should be mentioning that i run the N900 at 900mhZ at Lowvoltage profile the whole time. But still pretty amazing from the stock battery. And as im typing this, im still rocking 34% batterylife. (not been using the phone since I got home)

Thats just what i've seen so far, not really a good batterytest, but i just felt like sharing with you.

Kind regards,
Futtawuh