Almost always in Hot Questions on the StackExchange.com site there are questions from Math.SE, so I think it would be so much better to have these questions rendered correctly instead of reading the ugly stuff like this:
When it's not rendered it's hard to check with a single glance if that question is interesting for someone or not. So maybe you could load MathJax only if there are questions from Math.SE (or other scientific sites that are using equations) or something smarter just to make these interesting questions a little bit more interesting.
Edit: Just to make it more clear, I'm talking about adding MathJax only on this page: https://stackexchange.com/questions, since there are a lot of questions that are coming from Math.SE.