This may or may not apply to the KB talked about in this thread but it's the closest i can find.
I have a server at work runing Windows 2003 server. We have a shared network drive on the network that is housing 3,8TB (in just one share).
The files are spread out in different folders on the share, much like everyone would think.
The problem for me is that when using my Vista office computer transfer speeds are horrible. I get speeds as slow as 10Kbytes per sec, whilst using XP, speeds are normal (around 10Mbytes per sec).
I'm not sure what really is the problem but my best guess so far would be to say that maybe this problem occurs more often when the share is extremely large.
I have no issues coping files from other servers in our network, runing on a similar setup but with much smaller shares (50GB~).