This is a little userscript that adds MathJax to WeBWork using the MathJax CDN. It (is supposed to) work correctly for questions, answer previews, and even sidenotes ("Set Info").
It has been tested only on some of UCSB's WeBWorK installations, but it should work in other installations too (please send me a patch report or an e-mail if it doesn't). It also has only been tested in Google Chrome.