I'm curious -- it looks like there is nowhere on the application form to describe your idea. That is, you're not just letting people apply without an idea, you're stopping them from applying with an idea. Is that intentional?
This is a separate application form for people with no idea. You can still apply with an idea via the regular application form: http://ycombinator.com/apply.html
(There will be a FAQ about this sort of thing, but I wanted to get this launched today and only had 10 minutes to do it in before I had to go to office hours.)
We still prefer that people apply with ideas. All that's new is that we've added an option for people to apply without one. All else equal, a team with a good idea has a much better chance of being accepted than one without.