What do you all think of the above argument? It seems very convincing to me, but perhaps stronger forms of solipsism could be imagined that overcome Wittgenstein's private language argument. Of course, I'd have to be the one do to it if I wanted solipsism proved true, for it can really only be true for one person if it's true at all. And I'd only be proving it to myself. It would be empty and circular.
Oh, by the way, I'm David, and I'm not a solipsist, but I've always found the idea fascinating. I have entertained the possibility of its truth from time to time but eventually I decided that the conceptual contortions involved in such doubts were too daunting, and that it would make no demonstrable difference if I really were the only mind in existence. The consequences of my actions would remain unchanged, for from the fact that the world is exclusively my world, it does not follow that I have complete control over all that transpires within it. For example, I may be sitting all alone in my room, but I cannot make my desk levitate or have the walls suddenly turn orange, no matter how hard I may try. So being correct in one's solipsism does not make one the master of the universe, but merely the only conscious agent and observer in the universe. Knowledge may be power but it is not absolute power. Solipsism turns one into a kind of impoverished deity.
All that said, I find the fact that a community of solipsists or would-be solipsists exists on LiveJournal to be delightfully ironic.