Yes, indeed, and I'm not even sure what it means to say that one knows something. Epistemology has always fascinated me. There ought to be at least a few Quantum Epistemologists running around, don't you "think"?
You could look at it like this: every statement is ultimately self-referential, because it is never more than an indication of some brain state-- a particular brain state in some human brain, and the human brain might not even be reducible to a finite state device. And then where are you?