[abh19]

Couple of comments.

First, as others have said, it's a good idea to back up before major updates. Superduper! is great for this purpose—better than Time Machine—because if you run into a problem, you can simply reverse the process and in a few minutes you're back where you started.

Second, when you run into problems like this, try shutting down and rebooting the computer rather than simply restarting. You can also try to clear out some of the caches using a utility like Onyx (use the Automation scripts (the "cleaning" set)). Also, it helps to run Onyx periodically, like every month or so.

Third, which perhaps I should have mentioned first, run Software Update with no other applications (or users) running, especially for a major update like this one. Do a fresh log-in, holding down the shift-key to keep those pesky 3rd party background processes from starting and messing things up.