Another good point from EoC:
It's amzing to me that people are still referring to commercial banks and thrifts as "safe and boring operations," even though 140 commercial banks/thrifts failed in 2009, and the number of banks on the FDIC's "problem list" has risen to a whopping 552. Commercial banking is inherently risky — in all loans, there's a risk that the borrower won't pay you back. Just ask all the commercial banks and thrifts that lent most of their deposits out in the form of commercial real estate loans.
Another reason why having TBTF banks may actually be a good thing. For more thinking along these lines, see this discussion. There are some interesting ideas in there, although operationalizing this stuff might be difficult.