Don't know much about Thiel Fellows program. But I think just dropping out of college flat out to start a startup may not be a good idea. Unless you have been associated with something like a hackerspace where you've collaborated on projects with other like-minded hackers. I feel colleges are where it is a great likelihood to meet your potential co-founders, prospective employees, etc. To give more clarity, I don't think there is any question that Facebook's early success was due to all these Harvard grads/dropouts filling in the recruiting pipeline.