Completely agree. At worst you fail, but you learned how to work hard, you gained access to some awesome tech circles, and you will be better off next time. As long as you fail fast and learn from your mistakes there's absolutely no downside.
In the best case, you're Xobni or Loopt or Reddit or Scribd. Seems like a no-brainer.
We weren't 100% sure going in, but coming out can say it was absolutely the right move.