Valve has asked top clans to participate in a TF2 beta focused on improving 6v6 balance for leagues.  FakkelBridgade has the full story:

The project headed up by our great friend Robin Walker. The aim of this project is to get the competetive community to help fine-tune TF2 for competetive 6v6 play. We’re still at an early stage, nothing new has been introduced on the beta-client yet but the forums are up and discussions are already ongoing.

The first stage of the beta, as explained to us by Robin Walker. Will be to re-shape the sandman for future use in competetive TF2. This means we’ll be playing part of our normal match routine on the beta-client, behaving as we normally would. We all hope we can make TF2 an even better experience with this brilliant project!