In order for a pistol to be over-rated, the capability of the pistol must be thought to be higher than they actually are. But who decides what, exactly, the pistols are capable of? Some people(myself included) cannot shoot Glocks to save our lives. They seem like bulky hunks of polymer with the ergonomics of a brick and the accuracy of a Derringer. But then again, some people are dedicated to them, almost to the point of seeming like crazed lunatics.
I think all pistol owners, to an extent, over-rate their "baby"(Or babies). Some people to a lesser or greater extent. Some hold the Glock/1911/USP/S&W Revolvers/whatever on an altar, all powerful, perfect and untouchable. Some just think their pistol is better. Some over-rate some specific facet of the pistol, such as the trigger, the cost, the reliabity or whatever is their fancy. The truth is that no matter how much you rant, rave, froth and foam over a pistol, there will always be someone for whom it will not shoot well, will not function well, will not be cheap enough etc, ad nausem into infinity.
A thing that's value and performance is entirely or mostly subjective cannot be really over-rated, because it all depends on whose hands hold it.
On a side-note, I consider S&Ws, Glocks, Berettas and some 1911 variants over-rated. And anything pistol that costs more than 1000 US dollars.