I assume you're talking mechanics only? This board is awash with common issues on the 05+ Mustangs - the slow gas fill and skipping Shaker being prime examples.
Also, I've met people who get pissed about these issues, but don't do anything about them, so Service Depts see less action than they should. Crazy, I know, but I meet people all the time who seem to think the slow-fill issue is with the gas stations, and that the cd skip is a semi-normal issue (probably from experience of the good old days when cd players first went into cars and only didn't skip when the engine was off).
There's plenty wrong with these cars, and Ford knowingly propogated the issues found early on the 05MY onto the 06MY (haven't met anyone with an 07, so I can't speak to that).
Don't get me wrong, I don't regret for one minute buying my car, but then, I don't sit on issues I find with it. But saying this car is "well built" or relatively defect-free is simply at odds with the evidence.