I can put my whole library on Shuffle and get more coherent playlists than Genius, so i hate it because they spent their time working on this piece of junk instead of making iTunes better and faster.
I find Shuffle just plays an album with a few other tracks throw in then may go between two albums and move to a thirds and fifth before finishing off the first ones. Meh at least Genius gives me a more random feel. For me it works.
I never realised iTunes was slow to start with