Thanks for making Index Tank, I am just starting to implement it into my ruby application and have found it to be easier than any other search option I have tried.
It could be big, but I don't think photo sharing is the right platform for what they are trying to do. Facebook allows you to connect with people who know you, twitter lets you follow people you know, but the next big website will be the platform that lets you find people in your area that you don't know but should. Whoever figures that out will be a millionaire.
http://groupcourse.heroku.com We allow anyone to create a class in their local community about anything they love to do. With this demo you can sign up and post courses. Full application will be launching in June.
Background: Group Course is an online marketplace that connects students to teachers directly. We make it easy for people to sign up and create a course in their local community, we then advertise in their local area and take care of all the financials. If you want to take a class we allow a full refund if you don't like what you are taking in the first couple of days. For this service we take a 10% cut of the revenue that we generate.