If Samba is doing AD integrated authentication to a domain controller
that isn't on your local subnet this can also cause Samba to be
dreadfully slow, even with full Kerberos authentication working on the
Windows client and Linux server. Whatever Windows does differently in
this situation works. Based on how AD was structured when I worked at
the U my guess is this could be the culprit. I was never able to find
a fix other than get a local DC or move to a Windows file server.
Samba on Mac OSX has the same issue.

I don't see it as a step in either direction. A properly administrated
Windows server works as well as a properly administrated Linux server.

-- 
Andrew S. Zbikowski | http://andy.zibnet.us
IT Outhouse Blog Thing | http://www.itouthouse.com