I had been experiencing a problem with this site and another where when you visited using IE on Windows you would get a download dialog box asking if you wanted to Open or Save (not allowing you to view the regular web page.)

After some Googling around, found some solutions on the WordPress support forums:
Ie tries to download the blog.

In short, the solution to this problem is to hit your the wp-admin/upgrade.php page for your site. (I had experienced this problem on a couple of sites that had had WordPress upgraded. So, in short, remember, if you upgrade your WordPress installation, don’t forget to hit the wp-admin/upgrade.php page as a final part of the upgrade process.

That’s all it took — after clicking on that page, the site appears fine in IE on Windows.