Sam Sacks glancingly reviews Best New American Voices 2006 and quite reasonably takes MFA programs to the mat. Some, like The Elegant Variation, call these programs meatgrinders. The Literary Saloon snips the salient points. Which I'll summarize:
MFA programs churn out middling, formulaic writers.
Maybe MFA programs in writing are a little like studying jazz performance. You'll get a lot of practice, and with practice you get better. If you get really good, you'll be able to play in the backing band for just about anybody. You probably realize, as a jazz musician, that greatness comes from a crazy alchemy of risk and timing and the artistic dialogue you have with other musicians. Maybe you'll get lucky and be a long-lived legend, like Louis Armstrong; maybe you'll be mainstream and respectable like Winton Marsalis; maybe you'll be known by your peers and have some odd popculture breakthrough, like Herbie Hancock. But you know that you'll only be the next Charlie Parker or Miles Davis with a lot of luck and probably a lot of damage to your internal organs. Chance are, though, most everybody -- even some of the most talented -- will end up on the backline.
MFA programs help writers be pretty good but not great. Lincoln says they don't seem to affect the greatness to shit ratio you'd find anywhere. Who can expect them to do better? It's the writers who bear the responsibility to take the risks (both personal and artistic) that make their work interesting.
As many flaws as MFA programs have, they're part of a system that is somewhat functional. It's up to the wrtiters to use them for what they're good fort: contacts. And practice.