Looks cool, but you should make it a greasemonkey script, so I don't have to press it on every page.<p>Also, give the bookmarklet link on the page a better name than hn.js - to make a bookmarklet, the easiest is to drag that link to your toolbar, but that gives it a title of hn.js.
Looks cool...the font is a bit hard to read though. Perhaps you could add a bit of code in that checks the header link styles and uses those same background and link colors for the little popup.