Like most WWDC attendees, I immediately tried Leopard. After two days, several reinstallations and lots of crashes, I went back to Tiger.
Leopard worked OK when I did a clean install on my external drive, but I couldn’t use it for any real work that way since I couldn’t access any of my email, address book, iCal, or Yojimbo data. I decided to give it another chance by doing an upgrade install on my MBP (after doing a full backup, of course), which was only barely usable. For some reason blued (the Bluetooth daemon) would keep crashing and relaunching continuously which made Bluetooth unavailable. Also many applications including Parallels Desktop would crash immediately after launching. Doing an archive install didn’t work any better. Among other problems, the clock was very confused about time zones. The menu bar clock showed the time in PDT, but the date & time control panel showed it in EDT.
I spent much of the day yesterday reinstalling Leopard several times. Last night I gave up and restored Tiger from the Backup. My MBP is now back to normal. I’ll try installing it on my iMac when I get home.
As a lot of people have said, the translucent menu bar is a mistake. If you use a dark colored background, the menu can be very hard to read.