Viewing your pagesource and clicking on your first style sheet link brings up this error:
<html>
<head>
<title>Not Found</title>
</head>
<body>
<h1>Apache server with mod_pagespeed</h1>
OK
<hr>
NOT FOUND:http://mikewills.me/blog/links-for-2011-02-24/
wp-content/themes/richardshepherd-TwentyTenFive-a8f2860
/style.css.pagespeed.ce.pAcUzu9T3K.css
</body>
</html>
So it looks like your (cached?) stylesheet isn’t where you think it is or your apache module isn’t configured correctly.