Instant short-links is a nice idea, especially if you're aiming for the Twitter market.

Progressive enhancement would be good: the background doesn't render correctly in IE9 making the main text impossible to read. That applies to the homepage and the sign-up page. You'll lose potential users who will simply move on.

http://www.webpagetest.org/results/11/11/03/JS/22M02/1_scree...