I very rarely will say anything about a site if the only opinion I have is negative. Twingr looked like an interesting idea. The service let's you create your own Twitter-clone microblogging site, as does Yammer, but without any constraints regarding who you may invite. Alas, I can't say that I know what the experience is like because I couldn't get past the front door, so I walked away possibly never to return.
So here's the criticism, and my advice for how not to run a product alpha/beta.
1) Don't put a very prominent form to create an account on your front page if this is what you happens when you submit.
2) Don't make a second create button on the page (see bottom of the first screenshot) that does nothing when you click it.
3) Don't do all the above, blocking people from registering, and then leave out a sign up for beta form to remind prospective customers to come back. I won't remember ever hearing about this site and probably won't likely be back if not reminded.
First impressions matter, and I know it can be very difficult to recover from a bad first impression with a product. If I were these guys, I would make those few fixes real fast.