Supposedly the network stack was re-written for Vista. I imagine it has something to do with wanting to handle IPv6 natively, but that's all speculation on my part. However, I do have some first-hand interesting data from the past few hours:
I was cleaning up a machine, backing up files with a live Linux distro (Linux Mint, in this case), then restoring it to its original factory state. To take the data off, I am using an external Seagate drive plugged into my server, connected through ssh to Linux Mint as the OS running live off the CD. If this part sounds redundant, it's only because I want you to be aware of that particular fact: it's a live CD, running the whole OS out of the memory. Transferring the files off took about 20-30min, at 22-25MBps. This is pretty standard from what I've seen of 1Gbps in the wild. I'm not terribly impressed, as this is what it should do: transfer files as quickly as possible.
What throws me back is after the Vista re-install is complete, I'm transferring the files back to the newly rebuilt Vista machine... at a max of 7-8MBps! What is going on here, Vista? C'mon now, these are problems that should be solved! It's taking over an hour to do on an installed computer what a Live CD did in 30 min or less. Why, Vista, why?!?