Adobe Flash Player ungodly slow in OSX
I've been trying to figure this out for a while.  Here's the answer:

Chrome has a flash player built into it, and it updates automatically.  Other browsers use an external flash player.  If you're like me, you have flash player installed outside of chrome for other browsers.  Chrome doesn't seem to handle this very on it's own, but you can disable one or the other by going "about://plugins" in chrome, expanding the details (+ details at the top right), and finding the flash section and clicking disable on one or the other.

It doesn't seem to matter too much which one you use, but turning one off dramatically improves flash performance and overall memory usage for me.