My Photoshop was very slow today, here’s how I fixed it:
Cleaned the font cache in the font management app I use (FontExplorer X Pro).
Set the history & cache levels to Tall and thin (I work with a lot of files with tons of layers, don’t do this if you edit 100Mb photos).
Rebooted the system and everything was snappy again. Yeehaw.
(BTW, check out the recent sneak peeks at Photoshop CS6)