I used to get this problem on and off, but now it's mostly on. The TeX that I see doesn't have spaces in the right place, or something; it is getting really hard to read. I'm using Chrome 7.0.503.0 dev on Windows 7.
I can also reproduce the problem on Chrome 8. It's odd because on an earlier version of Chrome on a different laptop I encountered no problems, and once on this laptop the font loaded correctly. But then it went back to not working again. All fonts were downloaded, according to Chrome's resource tracker, but the spacing remains weird.
Anyway, I was able to fix my problem by installing the MathJax fonts locally. On Windows, you just need to download the fonts and drag them into the Windows/Fonts folder. MathJax detected that I had the necessary fonts locally so avoided any remote font problems.
Note: I've read here that sometimes MathJax might not be recognizing local fonts; in that case, I don't know how much the above will help.
Edit: I don't know how long this link will be valid, but using these fonts instead also work. These are the actual fonts that MathJax tries to download onto your computer (I think), so may look better than the other ones.