Just watched a video about Tab Candy for firefox and it's pretty cool. I've always wanted some kind of tabs management for Safari, I have 20 or so tabs open at any time.
Do you use Spaces?
I can't imagine that you have 20 tabs open at once that are all "related" to each other. When I've got that much going on, I'll group them and use separate windows, sometimes moving a window to another Space.