I know this is quite an old post, however I signed up for this forum because I've gotta say this expression has blown my mind. Check out this video I made with it last night, also tying in opacity to certain keys:
http://www.youtube.com/watch?v=Duqet_xBXBY
I haven't really played around too much with expressions but I'm obsessed now. I wish I'd taken more math in school, but I'm going through tutorials now. this is obviously a rough video and next I'm going to plug in this expressions to trapcode Form / Particular, I'm looking forward to seeing what it can do.
I also have a question - could anyone kind of break this expression down into what it's doing? how would I go about modifying the "default" playback rate or adding my own mods to it?