I've been using ratpoison a little on-and-off. Right now I'm using openbox on my debian box and compiz on my ubuntu box (with metacity replacing it when I play games).
I liked rp because it made me feel uberleet. It probably has a small memory footprint too. Most of the time, I have two windows open: screen and firefox; rp handles this beautifully. However, moving windows around is not very efficient with rp, compared to a non-tiling window manager. Also, I like the bling of compiz