I had installed ClockworkMod ROM Manager (free) from the Market, but decided I wanted to do this first one from the recovery image. The ROM Manager uses the recovery image anyway, so it shouldn't really matter how I do the next one. On to the results!
Holy. Battery. Life.
|Battery usage screenshot|
I can't show this in a screenshot, but the overall response of the phone is like night and day compared to Sense (in my opinion). Screens and menus load almost instantly. Apps load many times faster, and it feels like a real 1GHz device! Granted, this is a fresh install, so I haven't gotten it bogged down, but it is definitely faster than Sense ever was.
I strongly recommend that if you have an Android phone, that you root it, or give it to someone to do it for you. You won't be disappointed.