My professor who is the director of the mfa program at GMU told me that a MFA is good if you want to teach at a college level. Getting a MFA along with a published book (yeah or two) will get you into a tenure track professor gig while the MA in English won't get you that. He said basically you need a MFA or PhD to get a tenure track job. If that helps any.
It does. I, personally, feel that the only reason to get your MFA is if you want to eventually be a professor.