Well, it's already been out for a while but here is an invitation link just in case, it's free to sign up! Join Stumble UDON
stumbleudon does not work well. its a stumble exchange. i tried it and its not good. see this post on this forum to get the scoop and tricks ... http://forums.digitalpoint.com/showthread.php?t=815111
They bring low quality traffic and if you have a site which is aiming to make sales rather than generic traffic, don't use them.