othermaciej likely read Megan McArdle's article at (http://www.theatlantic.com/business/print/2011/10/if-you-fav...). It's a good article.
Although RyanMcGreal didn't refer specifically to Glass-Steagall, it's a good bet that "re-regulating" (i.e. re-introducing measures from that law) might be a bad idea in several cases, Regulation Q being one of them.