Okay, sorry for the late reply, but before submitting a bug, I wanted to check this behaviour further.
Over the weekend my N900 was under low, medium at best usage. I couldn't reproduce nor find the same strange power drain from the first day after the firmware update. Battery was "ok" for N900 standards and my experience.

Today I have the same working hours like thursday and my N900 is behaving normaly. Charged over night, unplugged at 4am and right now - as I am typing with it - battery is about 40%. And usage was heavier than before, two and a half horus MP3 via headset, quite some internet and youtube. Even downloaded three applications from Ovi.
So it seems like it was a one-time thing.

The only difference I can really recall from the day the power drain happened would be the Mediaplayer widget. It was enabled that day and after the drain I disabled it.

Other desktop things running:
OMweather widget
calender widget
quite some application shortcuts
a few contacts
four bookmarks
RSS widget with two feeds

RSS gets updated every 2 hours.
E-Mail every 1 hour.
OMweather daily.