SearchEnterpriseLinux has an interview with Samba Team member Andrew Bartlett about Samba4. The ground covered in the interview provides answers to questions like what is Samba4, what does it do, and when will it be released? Andrew begins with a basic introduction to Samba4.

Samba 4.0, on the other hand, is a far broader effort. The code will undergo major restructuring and hopefully emerge with more consistency. For starters, version 4 will emulate Microsoft Active Directory to Microsoft clients in contrast with Samba 3, which looked like Microsoft Windows NT only to the network, he [Andrew Bartlett] said.

For the whole piece see, Samba 4 hits alpha status, but 2008 release unlikely.