Looking forward to seeing what the first/final version of this looks like and offers. Definitely need this kind of service a lot. I was thinking about something like this ever since I heard them speaking of a social checklist app on http://techzinglive.com/page/1419/250-tz-discussion-rise-of-... . Actually I would strongly think about adding a way to share and find checklists, maybe even a checklist store for larger checklists (e.g. conference planning) instead of having to come up with every checklist from scratch.
Good luck and endurance!