I think I may have figured this one out. Or at least, I've solved it on my house network.

First, my situation: on my N800 with OS2007 a fully charged battery could remain connected (unlimited time) on my house wifi and the battery applet would report 10 day idle time and 7 hours use time.

I upgraded to OS2008 and on a fully charged battery the battery applet reports only 2 hours of use time.

My solution: change a setting on my wifi access point! I have a Netgear RangeMax WPN824 (firmware V2.0.10_1.2.17NA). On the "Wireless Settings" page of the admin interface I changed the wireless mode from the default (Auto 108Mbps) to (G and B) mode.

Blammo! instant battery life With unlimited idle time on wlan connections I'm back to 10/7 battery reports.