Since nobody has said it, the real issue with the GOM bonuses was that USAirways had several targeted versions (with promo codes) of the exact same offer, and people signed up for several (up to all 5?) of them. So a flight that usually would accrue only 500 preferred miles would instead accrue 3000 (500 + 5 GOM bonuses).
A bunch of people were getting CP on 2 flights when GOM was combined with some others. (Imagine a normal 5000 mile transcon R/T getting 30,000 from GOM alone, and then tack on some other bonuses as well). When people realized how lucrative it was, they tried not to talk about it too much on here.
Bottom line, USAirways screwed up in devising the promotion and not preventing all the multiple registrations. Then they (as usual) blamed the customers for abusing the system that they created.