CSS works fine. (Try this one: https://raw.github.com/twitter/bootstrap/master/docs/index.h...)

I suspect that JS that didn't depend on the page-load to trigger it would work too. I had never considered looking at JS-enabled pages though. When I wrote my bookmarklet, I just needed to view static documentation.

Edit: I found a page with only on-click JS events, and they didn't work. Oh well...