I've mentioned Chimney before. Now, a new Windows Update fix for TCP Offload, which turns it off.
It was on by default in Windows Server 2003 SP2, so if your NIC supported Offload, or RSS, or that other thing I can never remember, it was enabled.
But: we (PSS we) typically turn it off as a first troubleshooting step for any network-related issue -
a) because we know from experience that several drivers seem to do interesting things with it installed (that's a nice way of saying update your drivers),
b) because several of our drivers do interesting things with it (if you're going to choose to use it, check for recent-model tcpip.sys hotfixes), and
c) because we want to be able to see TCP traffic in a network capture for troubleshooting purposes.
Off-unless-opted-in brings parity with Windows Server 2008.