My biggest concern is over the recent 10.5.2 update causing my MacBook Pro C2D 2.16GHz to intermittently freeze when running on battery power (requiring a cold reboot).
Apparently, the issue is minor enough not to garner any attention but on the Apple Discussion Forums, there are many who are having this issue.
http://discussions.apple.com/thread.jspa?threadID=1390673
Leopard: Not Quite Right