In regards to the #8 (Dating) from list of ideas posted by PG: http://ycombinator.com/ideas.html
here's an idea.
have a dating site where users register, fill in profile, upload avatar etc. - but when they search for other profiles, the results are presented in an anonymous manner - so, for instance, instead of displaying avatars of users, display a default image. List only some aspects of the users profile (like interests / profession) and let users decide based on that if a certain profile seems interesting. If so, they can connect and only then, the avatar and other details are shown.
The fact that the photos /avatars are hidden can both serve as a pro and a con.
A con because profile pictures/photos are one of the most engaging aspects of such a site.
The upside of this approach will be that it will encourage only serious daters and at the same time limit folks from deciding based solely on physical appearance.
I'm just thinking out loud here, but would like to know what you think about it. If such a service already exists, my bad for posting this.
I think people care about how someone looks, whether they want to admit it or not. I think you're going to have a tough road to user acquisition if people invest their time trying to get to know someone online and then don't like the other user's appearance for one reason or another.