Oh, man. I had forgotten how awesome John Baez is. It's people like him (and like Tom Leinster with his book Higher Operads, Higher Categories) that the very existence of the web is vindicated by. Just ginormous quantities of freely available, fascinating scientific and mathematical material, reasonably organized and cross-referenced even within itself, and frequently updated. I should remember to go back and read more of his stuff the next time I need a good kick in the motivation pants. There are few authors I've read capable of tackling hard-core, down-in-the-trenches mathematics with the skill and discretion he has, sparing just enough details to make it followable (with some effort, cf. my earlier bitching about his "an introduction to n-categories" being hard going), but sparing few enough to make it genuinely exciting.