The problem isn't what they promise. The problem is when will you get what you were promised.
Last summer, BFL made a promise to deliver hashing hardware in the fall that sounded like an amazing deal. They still haven't delivered that hardware over a year later.
You would be wise to pick a company that can actually deliver product without year long delays.
Wrong again! Their ASICs are almost a year late, with 400% the originally advertised power draw. And to top it off they belittle their customers the whole way.
But sure, if you were going to flush the money anyway, why not pay BFL to **** on you instead?
Had they delivered their current specs in Oct 2012, I think people would have been tolerant of their failures in the power draw department.