I heard about this extension here http://meta.wikimedia.org/wiki/WikiGTD It sounds great, but i don't find any sourcecode or a working demo...
I too am interested it see it. All I can find was the extension author's blog is here but no sign of the actual wikigtd extension:
http://www.wikigtd.com/ and http://www.bradheintz.com/blog/
Al Degutis