You know man, you make a good point. Think about how long it takes you to take off a shoe, aim, throw, remove second shoe, aim, throw. If that had been a gun with a full magazine, even an amateur probably could have gotten 7 or 8 shots off in the amount of time it took the Secret Service to react.
I think the Secret Service kind of gets lazy. It's rare they ever have to actually DO anything (at least the presidential detail, I know there are some dudes who do way more than they get paid for). When is the last time we saw agents dive on a President? Regan? And before that - was it Kennedy?
They really need to step up their game. Especially with the circumstances they are about to be faced with in about a month.