Some information about Windows Direct Hosting (port 445) can be found at:
http://support.microsoft.com/default.aspx?scid=kb;en-us;Q204279
Here you will see that, by disabling port 445 (direct hosting), all traffic
reverts back to NBT.
>From what I can see, Direct Hosting is no more than SMB over TCP/IP, instead
of using NBT (NetBIOS over TCP) as an intermediary transport.
Blocking Direct Hosting should not break anything (it is merely a
'short-cut') but, once it gets implemented, it should reduce overhead on
server and network.
Kit