I actually didn't figure out how to do it in Less Wrong Markup, I just went into HTML mode, which doesn't seem to work for comments. So thanks for that.

The one issue with mouseover text is that it takes a pretty long time to appear (often longer than it takes to load a webpage). I'm not sure if that's a setting that can be changed in browsers, or is unique to individual sites, or what.

I've actually seen it used pretty effectively on some forums, where mousing over a thread title shows you the first few sentences of a thread. That would be a great feature for Less Wrong, if we made it a convention for the first few sentences to summarize the article.

Or... does this site have a glossary? That might help dramatically.