I hit an odd glitch yesterday where my wifi router stopped giving out DHCP IPs. It still showed it was available, and routed for devices that already had an IP, it just refused to give out new leases. (Most of my devices are DHCP, but are mapped by MAC and have a non-expiring lease.) When I came back from work I was around a few hours and my phone started beeping that it's battery was low. It apparently kept trying to switch over to the local wifi and ate a lot of juice doing so. Something like that would kill any device though.

Moral of the story: Sometimes it's not the N900 that's to blame for it's power usage. It could be someone nearby has setup a new wifi router or a bluetooth device that's constantly pinging your N900 and waking it up, making it eat battery.

Just something to think about.