The Rotation tool of Photoshop CS5 is one of the best inventions ever. I supsected CS5 wouldn't offer (to me) anything I really love but ... gods, I love rotation when I need straight(er) lines and it comes in handy if you need to ink or work neat.
More information by Adobe can be found here:
I know Painter had it for ages but as some people might have painfully experienced Painter seems to be unable to NOT crash. I mostly work with 600 dpi and I doubt Painter would have liked my game board with 2 m width and 600 dpi.
Hope somebody didn't know the Rotation tool and loves it as much as I do now :)