Upgraded last night, while I slept
Woke up to a pretty happy Mac this morning. ML informed me that I had one piece of incompatible software installed (SnapsPro X - which I don't remember installing, but whatever).
One annoyance so far: Messages. When I tried out the beta under Snow Leopard, it worked mostly fine but could not connect with the old version of iChat for videoconferencing that my parents' iMac G4 uses.... they haven't come online yet today, but that'll be one of the first things I test.
Ah, but the annoyance: They removed, for reasons known only to Steve Jobs' ghost, the menu item for Buddy List. It used to be that you could select the buddy list from the iChat menu bar icon, which resulted in iChat launching. Now that item has been replaced by "New Message...". Perhaps a minor thing, but I used that menu item frequently...