I chose to upgrade my 13" MBP, which is about 2 mos old, and was originally set up with a migrate from my previous mac (also Leopard). Took 35 min, went smoothly. The only "problem" that I've discovered so far was that initially the display brightness dropped to lowest level during the install process and had to manually be readjusted after boot, and I had a weird issue with two-finger gestures not working properly. Two-finger tap wouldn't bring up the secondary menu; I had to uncheck the two-finger zoom selection, close prefs, re-open prefs and check zoom again, and it fixed the two-finger tap issue. Weird. All else seems just fine. Geekbench score increased by nearly 200 points.