Adding -cache 8192 to the mplayer command line fixes the problems with stuttering for me. Also with -lavdops skiploopfilter=all might just allow you to watch 480p videos if you are overclocked, but with a significant drop in quality.

A problem I am having is mplayer is not responding to keyboard input when launched by cutetube. Is anyone else seeing this? I have built my own version of mplayer so it could be a problem with that.