Just a quick reminder that websites should check for XSS holes on their site, especially freeform text input such as search boxes. Even big sites can have these issues with XSS and escaping user input. (Note: don’t click on these search results.)
If you’ve noticed that your rankings in Google seem to be affected, you might consider a few searches on your site to see if anyone has injected spammy or porn content on your site. If your domain was example.com, you might want to run a few queries such as [site:example.com porn] or [site:example.com biaxin] or [site:example.com viagra] to see whether you run across unexpected results.
Added: (Switching from XSS to pure hacked sites for a moment.) Make sure to change your admin password if you update (say) your WordPress installation. Sometimes hackers are smart enough to save your password and come back even after you’ve fully patched your system. I tend to change my admin password at least every time I upgrade my version of WordPress.