Usually when people talk about cross-site scripting attacks they refer to someone posting malicious code to a website in hopes of exploiting the browser vulnerabilities of other visitors.

What's often overlooked is using the visitor to submit bad information to a vulnerable script on (or off) the site. This is easily done through adding a link with some extras attached to the query string, or adding a form with a few extra parameters. Maybe those buttons you click on people's homenodes could be sending less than nice stuff to certain scripts?

Of course, if everyone was adequately paranoid and Didn't trust user input, this wouldn't be as big of a problem as it is.