OutCast3k, congrats on the release! We talked about it awhile ago on IRC, I'm glad to see you released it.
Also you might want to look at
http://www.bitrated.com/ which does the same thing but requires an account and has some other features. I don't think it can be easily used with an online auction site, like bitmit.net with multisigs. Your site seems much better for that.
It doesn't do the same thing; Coinb.in has a general purpose tool that can be used for many kinds of multi-signature transactions, while Bitrated was created specifically to facilitate arbitration services and has an interface that was optimized for that purpose. Also, Bitrated does not require setting up an account - its optional and only for arbitrators that wants to be listed on the website, and buyers/sellers don't have accounts at all (and I believe it should be quite easy to use with something like bitmit).