One problem related to engine belts and pulleys has been reported for the 2007 Ford Mustang. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2007 Ford Mustang based on all problems reported for the 2007 Mustang.
Harmonic balancer/crankshaft pulley came apart on a 2007 Ford Mustang v6 while driving. It had less than 37000 miles on it. Luckily, all that happened was serpentine belt slipped off, which I realized immediately when I lost power steering. I was near home and got home safely. This could be a major problem if it happened at highway speed. Replaced by my mechanic, who says that he has seen this numerous time in the past, and that Ford now sells an "updated" part for the vehicle. This suggest to me they know there is a problem, but don't want to pay to replace it.