With the IndyMac fiasco we had a couple of weeks ago I've been looking into what happens if your bank fails. This Washington Post article does a great job explaining things. Basically not having all your eggs in one basket is a good idea but there are safety measures in place.
"If you have $100,000 or less in your name in any one bank, you have nothing to worry about. The Federal Deposit Insurance Corp., an independent agency of the federal government, will insure up to $100,000 per depositor per insured bank or savings association."
What to Know About Your Accounts -- The Washington Post