Oh, I sorta forgot to mention: most games I have are playable. It's really the 'special controls' games, like Star Wars or Spy Hunter, that I won't play. However, Paperboy is playable using my spinner for x-axis, and P2 stick in right hand for throttle, with the upper-left button underneath my right pinky to throw papers. I've gotten to Sunday with this set-up.
Then of course if you have at least one U360 on-board, you can play analog/hall effect stick games - but some of them I think are a wash at best, like I, Robot. Road Runner, on the other hand, requires it. Unfortunately, the game is pretty boring after about 30 seconds and gets worse.
Oh, and lastly there's the dual-stick, dual-player games, like Smash TV or Splat! (love that game) that are fun alone but not 2P playable unless you have a dual-dual-stick panel. Just gotta.