Just did it, I'll update the userscripts site with it in a sec once I find a place to plugin my laptop. The code is below, the basic gist is that every 5 minutes, it will scrape your ignore list and store the usernames of everyone you ignored, then will parse forum index pages and hide any threads started by those users. It only parses the ignore list every 5 minutes to cut down on the ajax requests it makes.
Code:
// ==UserScript==
..snip..
Also, you will probably see a brief flicker of the user's threads every once in a while while it's making it's request. There's basically nothing I can do about that, sorry.