Search Opensource has an article on the Samba Team's current work with Samba4. Our own Andrew Bartlett is interviewed extensively throughout the piece.

"We believe that just because a company may choose to run Microsoft Windows as a desktop OS [operating system], they should not be compelled to run Microsoft's servers," said Andrew Bartlett, a member of the Samba Team, a group of about 30 people from all over the world who contribute regularly to Samba.

Samba 4 is about expansion. It expands Samba beyond its Windows client-based file and print sharing roots into new roles by bringing greater Active Directory (AD) functionality than Samba 3 offers. Greater authentication and a new role as a login server are also coming.