With great power comes greater responsability

This is, when you use cool stuff like AJAX, that empowers your website, you should take into consideration all the problems that it might cause, specially cross-site scripting.

I’ve been subscribing an interesting blog on security, GNUCitizen. I really enjoyed the Pownce Exploit they did, and shows that you might not be secure in all those websites you visit.

Oh, and you should really take a look at their introductory presentation on client side security.