Summary: ClippyML is a simple web browser that uses the system clipboard instead of URLs. Simply paste some text into it to see it displayed as HTML.
keyup event as this will put unnecessary load on your server. Instead, the thing to do is to wait a little while after the user's last key release to see if she's stopped typing before firing off a request.
I'm sure that there are hundreds of code snippets lying about for doing just this, and that JQuery probably already has something built in or a plugin for it, but a quick Google search didn't turn up anything for me so here I am, sharing my simple solution for delayed Ajax validation in JavaScript.