Both MathJax & ChatJax freeze my chrome and IE7 browsers running on Windows Vista for at least 2 minutes while it loads. The entire bowser is unresponsive, I can't even click on the start; sometimes the pointer doesn't even move.
I think this is a somewhat general problem, as the site can be quite demanding on resources.
See these meta.math.SE questions
A propsed solution (yet for firefox), is turn of harware accelaration of the browser. Something analogous might/should exist and work for other browers, too.