I finally called Apple tech support. I had installed SL twice but Mail, Safari, Logic and lots of other programs were repeatedly crashing in SL. It turned out that I had a defective installation DVD. The Apple store swapped it out for a new one. I ran the installation procedure again and this time everything seems to be working okay.
So if you're experiencing odd behaviors or crashes from SL, get a new disk.
So if you're experiencing odd behaviors or crashes from SL, get a new disk.