I still use plain ole CS but I get slow downs from 3 things:
1 lots of patterns, brushes, styles, etc loaded into the presets
2 lots of layers
3 not allowing PS to use enough hard drive space because it is pretty full

Buying a new pc with a larger hard drive fixed number 3 but I still get the problems due to 1 and 2 so I remove presets every few months and flatten things when done with them...although I'm sure you know about these work-arounds as well. BTW, guess I'll wait until CS5