I am sure you are all are intimately familiar with the problems with the Scalable Networking Pack (SNP) including it's use of the TCP Chimney feature that I blogged about at http://msexchangeteam.com/archive/2007/07/18/446400.aspx.
The problems that surfaced due to these features being enabled by default in the Service Pack 2 release of Windows 2003 brought out the worst in some network card drivers causing all types of connectivity related problems and crippled some organizations.
After some time, a hotfix (http://support.microsoft.com/kb/948496) was created to disable these features by adding the appropriate registry keys to a server which then required a reboot to get the SNP features disabled.
As of 8/27/2008, a new hotfix (http://support.microsoft.com/kb/950224) has been released to help address some of the commonly reported problems with relationship to Chimney and RSS for Windows 2003 servers. As more companies deploy Windows 2008 and Vista, it is crucial, or in my opinion, critical that this hotfix be applied to all Windows 2003 servers that may communicate with these operating systems. One of the main reasons is a new feature called TCP auto-tuning which makes use of RSS to expand and shrink the sizes of your TCP window to increase/decrease throughput based on current network load. This feature greatly increases throughput on your network, but if there is an underlying problem with the network card driver or any of these features between disparate systems, you may experience slower than normal network performance. The good news is that the Chimney feature is disabled by default in Vista/Windows 2008.