I have a 12' Field and Stream sit on top yak that I do a fair amount of fishing out of. I'm not a super heavy guy and notice that it doesn't track very well if I don't load down the front and back of it.
I have been looking a lot at higher end stuff, as I really do enjoy it, but things that are simple from a boat are complex from a kayak. Unless the water is totally dead, sometimes just lining staying in position to keep casting is a real pain, and it is pretty hard to adjust with a paddle while holding a rod. I would imagine fishing a huge open body of water like a salt angler would make this less a hassle, but when I'm trying to bass fish structure it can be a nuisance. I can't stop looking at Hobies with their paddle drives.
I bought mine a few years back and even when I get frustrated fishing out of it, I enjoy the kayaking side of the experience immensely.