Flash can have it's place in the fiery depths of hell. It's just so poorly coded and such a resource hog that it shouldn't be used anywhere, ever, until Adobe gets its head out of its ass and fixes the damn code.
There is no reason a 6 month old MacBook Pro with a C2D @2.8GHz and 4GB of RAM should exhibit slowdown on any website. (And yes, I know I'm walking right into remarks about "well, that just because it's a POS Mac")