I just updated my Pre to WebOS 1.3.5 and tried out Classic. Classic loads up fine and hasn't crashed so far, but Bluetooth Hotsync initially stopped working. The Pre would pair up with the laptop ok but Classic couldn't interface with Palm Desktop. I restarted the Pre. Then I tried out WiFi hotsync. This worked. When I tried hotsync via Bluetooth later it DID work. Hooray.

Moral of the story: Don't give up if you're having troubles with hotsync after updating WebOS.

Now I just hope that Classic is more stable in 1.3.5.