Apple has always seemed to give poor performance for remote users compared to an equivalent Windows setup running over the same remote link. I think this is a combination of several things.
Firstly, the Finder on a Mac gets a lot more information to display a directory listing than Windows Explorer on Windows does. The Finder is of course getting the same file/folder names but in addition can get Finder comments, labels (colours), custom icons, etc. which Windows Explorer would not.
Secondly, I am convinced that AFP is not as efficient over slow links and/or high latency links as SMB.
Thirdly, I am also convinced that the Finder is grotesquely inefficient in sending and processing commands and replies, whereas perhaps Windows batches things up. As an ancient example of this anyone else remember the floppy disk shuffle on the original Macs?
I suspect because Apple have a very fast pipe to the Internet they have not appreciated how bad this can be. They need perhaps to consider getting a WAN link simulator and then they can see the problem and hopefully introduce more optimisation.
Unfortunately there is not much you can do about any of these things, you could try using SMB on the Mac rather than AFP as this might cause the Finder to not try getting some of the extra information like colour labels. Avoiding using the Finder if possible is the best option, you could help achieve this by keeping shortcuts to files on the Server so you don't have to keep browsing to the folder itself.
Thanks John, and I hear SMB is going away in Lion? hmm I wonder if "fixing finder" for quick folder browsing is on apples agenda at all. Probably not. Oh well. this makes file sharing across vpn un-useable for my users.
insert frowney face here:
there we go.
SMB still exists in Lion and in fact is a 'new' written by Apple version supporting the latest SMB2 protocol. Apple call it SMBX since the old one was called Samba.
Unfortunately at the moment Apple's new SMBX is very much a version 1 (literally) and has many rough edges and missing features.