snow leopard 
After NOT updating to 10.5.8 (I was stuck on 10.5.6.) I upgraded to SL today. Here are some experiences and also open issues:
Installation on my late 2008 MacBook Pro (5,1) took less than an hour.
After Installation, Software Update downloaded two fixes. One was a new bt firmware.
Everything seemed to work fine. Expected battery time was and still is low.
That seems to be caused by a heating issue. SL keeps my CPU about 10C higher than Leopard. I could not identify a reason for it and other users have made the
same experience.
Other problems I had:
- After having run a time machine backup, the time machine buddy widget somehow become source of trouble: The whole dashboard got stuck and I delete com.dock.db and .plist but finally removing the widget seemed to fix it.
- Printing: The installed network printer (Canon iP4000 with Gutenberg drivers) did not work. Clearing it, adding it again as new ip printer and changing the driver back to the Gutenberg one made it work.
- growl is not fully compatible
- truecrypt cannot create new containers
[Update] The heating issue mentioned above did resolve itself after a
SMC Reset.