Microsoft AJAX & Google AdSense
I was bitten by this bug that was introduced in Microsoft AJAX RC. It seems that Microsoft AJAX is overriding the default implementation of Date.parse from Javascript with it's own implementation. Normally this isn't a bad idea, but it only accepted a certain set of templates when parsing making Google AdSense break upon loading on the page. Luckily enough, some developer named Cyril has a workaround available. The forum post and his blog entry (in French) have more information. Those visiting my website should no longer have a Javascript error displayed as I've implemented this workaround temporarily.