[mattmcknight]

I think what GMail did for conversations in email,GBuzz does for conversations in Twitter. The @reply mechanism and the retweet convention never really worked well for me in Twitter, although that may be because I was not using the necessary third party tooling to visualize it.

Also, you can add more than 140 characters, real links, pictures, etc. You lose some of the public version of SMS feel that Twitter has, but those constraints were becoming more of an annoyance to me.