I like the idea - I'm a big fan of the Seinfeld Calendar method of forming habits - although in practice I find that I end up using a piece of paper for my calendar.

I'm not sure if it's intentional, but it seems weird that you can't change today's status from completed to "good" to "bad". That make sense for positive goals ("I will do X"), because once you've done something you can't undo it, but it doesn't work for negative ones ("I won't do Y") - since you might end up doing that thing after you've set your status, and want to go back and fix it.

If you're looking for a similar service, check out Joe's Goals (http://www.joesgoals.com/). The interface is nowhere near as nice, but it allows you to have a few goals going at once and track them with more granularity than Seinfeld's initial concept.