Jonathan Agosta answered our call for an explanation of the nsmb.conf file and how it can fix slow SMB (also known as Samba) file browsing in Macs. He explained the tip about using the file to turn "notify" off, and why it might not work for all users. He also describes several other configuration tips that we've reported and thinks making these changes on a Windows Server instead of the Mac could be productive.
The nsmb.conf file contains settings (If it doesn't exist defaults are used) to configure the Network Protocol for Samba. The notify_off=yes setting will disable the Samba Notify-Change feature which is used to dynamically update the client's listing of files/folders as they are changed. (I have attached references.)
This can have a very noticeable impact on SMB file shares containing a large number of files and/or for those who have an environment where there is a lot of activity and changes made to the files. This is also why it does not affect certain users, especially those with more static content or few files.
The interesting part is that searching for problems on the Microsoft site leads us to KB885189 which details how to make changes on the Windows Server, but it also explains part of the reason for the delays being the increased number of TCP ACKs, which ties back to the tip "TIP: ACK! Slow Mac access to Win servers -- a server workaround " and also the tip "sysctl, ack=0", so what I am getting to here is that KB328890 is likely to be the proper, server-side solution to slow SMB shares from a Windows environment. (See also KB981482.)
I am in the process of testing a combination of these (TCP ACK=1, Notify Change=Off and TCP Autotuning=Off) on a Windows Server 2008 that is serving several Macintosh computers as well as Windows PCs, and where we have had complains about performance. I have high hopes as these three validate a large number of the tips and workarounds posted on www.macwindows.com.
Note that previously, another reader suggested editing nsmb.com to include "streams=no", a tip that had been confirmed. Agosta doesn't address this one.
If any of this information helps