One of the biggest problems with Frog-fishing is the frogs themselves. Not many good ones out there. First problem is the double hook. I don't really know why but double hooks are just lousy. Back in my steelhead days I tried double point hook Salmon flies and they were lousy for hooking. Maybe its having to drive two points in instead of one. Whatever they are lousy.
The other thing is that most of the frogs are too light so when bass hit em they bounce into the air instead of the mouth. You can weight em down, but its tricky because then they sink through the slop.
Then there's the problem of getting them to land rightside up. It really pisses me off to make the perfect cast (which I do every now and then) and then having the frog land upside down and get a wad of cheese stuck on it. Some of the Japanese frogs are designed pretty well in that regard (counterbalanced), but they still land upside down too often for me.
The final problem for me is that its pretty much impossible to find and target individual fish. You just gotta go out and pound the cheese. Gets really boring which is really the reason the hits seem so exciting. Just when you're about to fall asleep Kablam! and then you're supposed to not strike until you feel em pull???
Anyway back to the original question. There are guys out there who specialize in it and do pretty good from what I hear. They even catch some 10+, but fishing in CA there are a lot of better ways to consistently catch 10+ bass in my .02.