I love jsMath and MathJax, but there's a peculiar problem I've run into with using them. Unless I'm terribly mistaken, both require a few files to be placed on the same domain as a page using the toolkits. This makes it hard to use them with, say, Blogger or WordPress (running on a shared server, anyway). Since blogs form an important channel for discussion, I would have hoped that this problem would be tractable, but so far, I've not run into a good solution. That said, I wholeheartedly agree that such toolkits are a good way forward, as they allow for LaTeX to be used as an intermediate, author-facing language, and yet retain the benefits of standards-compliant web technologies.