Tweexchange is an interesting site since they claim no part of the transaction they are helping form and make no money from it seemingly:
tweexchange uses Twitter’s API to search for available domain names and then displays them in an easy to use interface. We cannot guarantee the accuracy of any names that show available and thus accept no responsibility for any inaccurate information.
When exchanging any Twitter names you have seen listed on tweexchange, you accept full and total responsibility to take care of all matters away from the site, with the full comprehension that it is against Twitter’s terms of service to ever buy or sell Twitter names.
So has this really worked? If you believe this link they have on the page, then yes it certainly does. I typed in my name and it showed it was taken but a bunch of names around it (much like a domain registrar would to sell you one).
Now it says you can list your own Twitter username, but you must provide your Twitter username and password to do so. This scares the crap out of me, since they do not broker the transaction, why would I log in as myself? Could they take ownership and broker? Is there a transaction fee? They could offer to validate a code you tweet to show you actually own a name instead. (notice I am giving suggestions and not just complaining).
A lot of questions but it does show monetization around Twitter once again.