There is a great channel 9 video that talks about the improved TCP/IP stack in Vista/Server2k8 (Longhorn), unfortunately, I spent about 15 minutes searching for it without finding it.
It is important to note that the share you are copying to is on a Server 2008 box, you only touch on it briefly. If I remember correctly from the channel 9 video, Longhorn is required on both ends of the file copy to take full advantage of the new network stack. This is actually a test that I have been wanting to perform, I think it would be interesting to see the speed difference when copying from Longhorn-to-Longhorn, Longhorn-to-XP/2003 and XP/2003-to-XP/2003. I am also curious to see if the file transfer utilities in programs like VNC and PC Anyware will benefit from this. I imagine they will because this all happens at a lower layer, doesn't it?
I think that this has the potential to save great deal of time for companies that do a lot of transferring to remote sites over WAN links. Thanks for the great screencast Michael...
EDIT
The video i was thinking about was actually a edge video, watch it
here.
This channel9 video talks about it too..