At first, I upgraded my iMac Leopard system to SL and it had a ton of problems. So I wiped it all clean with a fresh install of SL and that was a magnitude more stable. Unfortunately, bluetooth is (still) just awful. It had started to improve under Leopard but with SL it's unusable. I used a bluetooth keyboard and mouse and they were more or less ok most of the time. If there was any network traffic, however, the pointer slowed to the point where it jerked around the screen more than it followed the mouse. In addition, now and then it would totally lose track of the bluetooth hardware and I needed to do a PRAM reset to use it again. Leopard never did that. The "fix" was to buy wired hardware and hope bluetooth is once again usable some day. The system, overall, is noticeably faster than Leopard, however, so I'm keeping it.