Edit: I've put a lot of work into the comment below, so I would appreciate if you'd read it and respond to it. I know it's harder to discuss the specific provisions of Glass-Steagall and its affect on the market place than just saying "oh, the Glass-Steagall repeal is responsible for everything wrong". However, if people are going to cite the argument so often that it becomes the commonly accepted viewpoint, then it ought to be incumbent on them to UNDERSTAND it. Anything else is hand-waving.
I hear this a lot, too, but it's hard for me to see how the Glass-Steagall Act repeal had anything to do with the current crisis. In fact, deregulation seems to have mitigated the damage. The reorganization of Bear, Merrill, Morgan, and Goldman would have been impossible were the Glass-Steagall Act still in full force. They would have all gone bankrupt or had to be rescued by the government. Many of the entities that are in good financial shape are the large financial conglomerates that would have been illegal were G-S still in place. Customer bank deposits provide a stable source of funding when lenders are skitish. Reducing the supply of capital in an embattled industry would be the height of stupidity.
Many foreign countries never had any law like Glass-Steagall in place and they don't seem to be suffering the same problems. As logic tells us, the current crisis seems to be orthogonal to the presence or absence of Glass-Steagall.
Mcardle also had a wonderful post FACTUALLY summarizing the provisions of Glass-Steagall and its relation to the current crisis:
http://meganmcardle.theatlantic.com/archives/2008/09/clear_a...
I also addressed this issue on my libertarian blog a while back:
http://distributedrepublic.net/archives/2008/09/22/the-end-e...
A large problem during the Great Depression was that the United States had laws that artificially limited the size of banks (see "Unitary Branching Laws"). The result was that institutions in the United States had smaller financial cushions in crisis time and were more likely to go under. The United States suffered a FAR higher rate of bank failure than other countries, and states with unitary branching laws had higher failures than those without.
So I know blaming the Glass-Stegall repeal for our current problems is popular(populist) wisdom, but it seems to me that popular wisdom is, as usual, wrong.