When in doubt, create a new bubble. That seems to be the motto of Alan Greenspan and Ben Bernanke, and now the Fed is about to try to join Obama's re-election campaign by creating yet another bubble in U.S. Treasuries and mortgage-back securities. (Yeah, you know those things that lost their value a long time ago.)
Asset bubbles form when buyers force their prices above anything that would reflect their fundamentals, and when the Fed purchases these assets in order to support its "monetary easing" (a euphemism for printing money), it has to pretend that they are more valuable than they really are. Paul Krugman disagrees that U.S. bonds are overpriced, but as I see it, the Fed is in the process of creating new bubbles that are dwarfing what happened in 2008.