I second that.
Wolfire is a great example of this. They released an alpha version extremely early in development. Even without a “pretty” UI (and still without a pretty UI, tutorial, or missions).
As a result they continuously get funding and awareness of their game (and keep their backers happy).
With a very rough alpha version in hand I can show the game to my friends, and build hype which leads to more buyers. I can also provide you (the developers) with fearless feedback to make this game superb.