I generally prefer to use tcsh rather than bash. This is mostly because I'm a technological dinosaur. I also have a lot invested into my ancient and extensive .cshrc that has taken years to grow and develop.
Normally, I set the default shell inside the Terminal app preferences. But there's a problem. Snow Leopard keeps losing my preferences for reasons I do not begin to understand. With this Snow Leopard bug, I had to find another approach for choosing my shell. Terminal preferences were no longer going to work for me.
There are actually two very good ways to handle this problem.
First, there's chsh, as pointed out by Richard Buckle and Brian "Shmit" this morning. A command line utility, chsh edits the OS X user database, allowing you to change a user's default shell. chsh is built into OS X, and you can pull up a man page to read details about its use. Supply the shell you want to use, authenticate, and you're set. There is, however, an easier solution.
It's System Preferences. As Bill Bumgarner and Jordan Breeding reminded me today, you can access advanced user settings by right-clicking (or Ctrl-clicking) a user name in the Accounts settings; then choose Advanced Options. (Please note that you must first unlock the settings before this trick becomes available.)
When selected, an Advanced Options screen appears. You can set the new login shell in this screen. A simple pop-up list offers easy access to all installed shells. Select the one you want to use and, once selected, click OK to dismiss the screen and return to the Accounts settings pane.
This solution works a lot better than the bash .profile approach I had been using for a few weeks. Running tcsh through the .profile initialization file had caused an extra layer of interaction each time I wanted to close a terminal window. The application warned me that I was about to kill a running process (i.e. my tcsh subprocess). Changing my default shell meant I could create and close windows on demand without that extra dialog, a welcome respite.
In conclusion, while I'm not sure why Terminal keeps losing its preferences, I'm pleased that I at least learned a way to bypass the shell issue. Hopefully, Apple will get this bug fixed soon.