Mike recently announced the latest release of D3 as major version 3.0 with a large number of enhancements.
Chief among them appears to be a focus on transitions...
...and Jason Davies geographic projection manipulation.
The examples are fantastic and should be visited to get a feel for the different possibilities that they provide to an already awesome framework.
The examples used in the D3 Tips and Tricks document already use version 3 in the code, although they certainly don't utilize anything like the complexity available :-).