Seems like having an animated anything on your wall is going to kill the battery a lot quicker. I haven't used or tested the theory but does anyone have any confirmation on this?
Live wallpapers use a little bit of processor to run but it's not a huge deal... you might notice a small difference in battery life but you gadda take into consideration the "eye candy" human factor....
When I first got live wallpapers I had the screen on a lot more and played with the settings a lot more, changing wallpapers to see how they look, and I figured out it was me who was draining the battery because I wouldn't leave the damn phone alone... it's not so bad now that I've gotten used to it and leave it alone...