Here are a few things you can do (or not) that might improve your experience with Mac OS X “Lion”:

Nine Things You Should Do After Installing OS X Lion

While searching for information on the lock-ups, I came across a couple of posts on hints.macworld.com that suggest many (perhaps all?) of these spinning beach-ball cursor issues are because of interactions between the Finder and the Airport (WiFi) code. The suggestion is that the Finder becomes blocked when a connection on the local network becomes unresponsive.

One hint says the Airport icon in the menu bar is still active when the system busy cursor appears and that turning off the Airport, waiting a bit and then turning it back on gets things back to normal. If you don’t have the Airport (WiFi) icon in the menu bar, it can be turned on in System Preferences (but leave it on, or it will not be there when you need it).

Making Finder BeachBalls go away without rebooting

While the hint attributes the problem to “old Macs”, clearly if unresponsiveness is the problem it could be any number of things (e.g. putting the Mac to sleep).

The other hint doesn't attempt to guess why the hint works, but indicates about a 50-50 success rate. This hint only applies to MacBooks (and MacBook Pros). Put the Mac to sleep by closing the lid and waiting for the light on the front to start flashing, wait a minute or two longer and then open the lid to wake the Mac up. I'm probably not going to test this out as I run with the lid on my MacBook Pro closed all the time!

Another way to recover from application freezes

I'll wait (hopefully a VERY LONG time) for the next spinning beach-ball cursor and then try the Airport trick to see if it works. In the meanwhile, I'll resume my paranoid, save-my-work-much-too-frequently mode of operation — at least until I gain some confidence that Lion is, in fact, stable.