Link verifier bookmarklet / Greasemonkey script

Create a bookmarklet that, perhaps in concert with a Greasemonkey script (to spider to off-site links) processes all a[@href] tags in the page invoked on, checks whether they work, and mark those that did not, for instance with a style.textDecoration = 'line-through'.

Hm. Or maybe even a Greasemonkey script which does that and gets invoked via the greasemonkey menu scripts can register themselves for.