What are some theoretical explanations for deviations from the efficient market hypothesis?
I think this piece by John Cochrane represents a typical defense of the efficient market hypothesis from this kind of critique. Here's another. The basic summary is that market efficiency does not imply that expected returns cannot vary or that bubbles will not happen. Bubbles should be unpredictable, and variation in expected returns should be driven by risk or discount factors. Whether that's the case for the financial crisis is definitely a matter of debate.

Do people believe in efficient markets? I think that varies a lot from field to field. It might be more useful to say that efficient markets are usually the null or prior that academics in finance and economics work with when they try to understand something. That is to say if you want to use some data to try to convince them that financial markets aren't efficient, you face an uphill battle, but the struggle isn't impossible.