It's probably already in this huge list somewhere, but I would really appreciate it if right-clicking on the play button would just stop at the end instead of auto-rewinding. It should probably be optional (in case I'm the only weirdo who wants it this way ;)).
EDIT: I forgot to mention the dilemma of how to handle right-clicking when the head is already at the end of the time-line. You could have it restart from the beginning, but sometimes it might be nice to be able to go from somewhere in the middle to the end. In that case, you should probably save the head position when play is right-clicked, and rewind back there if it's right-clicked again with the head at the end. Just my two cents...