Broadcom finally has decent drivers that properly support the Scalable Networking Pack

When implemented correctly, the SNP is a win for performance and scalability. The SNP used to be an out-of-band download for Windows 2003 SP1 and then was integrated into Windows 2003 SP2. Unfortunately, most problems, especially related to Exchange servers, with SP2 have been due to buggy networking drivers.

In the past, the NDIS drivers were tied to one CPU. The SNP opens up processing to multiple CPUs. I suspect, but have no proof, that most of the problems we have seen with SNP has been due to older driver code not being very SMP safe. It reminds me of the nightmares I had with the SoundBlaster Live on multi-CPU machines under Windows 2000 and XP.

Anyway, as noted here, the Broadcom cards, which typically were the worst offenders, have updated drivers that finally have decent SNP support. You no longer have to 'cripple' your networking stack to keep your server stable.

A snippet from that updated post:
Previously I did not mention what network cards were affected, but the majority of the cases that we have seen have dealt with Broadcom cards or network cards that have a Broadcom chipset in them.

Broadcom has provided an update to their drivers and can be downloaded from here that helps resolves the issues with these offloading feature problems. To determine if you have the correct update, you need to check the version numbers to ensure they are 3.7.19 or later. Anything lower than that does not have the fixes in them. ExBPA is being updated with a new rule to detect if the Scalable Networking pack features are enabled on the server.

NOTE: Before updating directly from Broadcom's site, I would recommend checking with your Server manufacturer first before applying the update directly from Broadcom as this may affect your ability to apply updates directly from each vendor in the future using their integrated update utilities.

Currently there are only a handful of manufacturers that have updated the drivers on their sites, but over time, you will see the updates available for downloading.

I have personally dealt with cases that having the Scalable Networking features enabled with the latest drivers have not caused any connectivity issues to/from Exchange servers, so you can now take advantage of these features that may help increase overall network performance on your servers.