I upgraded from Karmic to Lucid some time ago and while I've generally been satisfied with the experience, my battery life went down from 7-9 hours all the way down to 3-5 hours.
This is quite an issue considering we're talking about an eeePC, which is supposed to be an unplugged device.
My suite of manually installed packages hasn't changed in any substantial way and my usage habits haven't either.
I've tried using powertop to squeeze out some more life out of the battery (which I pretty much never did before) but no big increases have been noticed.
If you need any data to solve this mystery, I'll provide it as soon as possible.