hmmm... I read either on mashable or techcrunch that tweetmeme was changing focus to analytics since twitter decided to do the retweet. Never saw anything about them working with Twitter.

Found the link: http://techcrunch.com/2010/08/12/twitter-tweet-button/

I do see mentioning of an agreement with Twitter but it is my understanding that Twitter has a licensing agreement to use the tweetmeme technology not that tweetmeme will be powering everything.