We recently resolved a particularly tricky issue relating to instability with both the Small Business Server and Standard editions of the Windows 2008.
In each instance, the server would be stable for quite sometime and then networking would stop. Sometimes, the server would freeze requiring a cold restart.
We had help from many sources on this; Microsoft posted two hotfixes (here and here), Trend issued updates for WFBS as well, but none of these resolved the issue. Other third party software partners also lent a hand to research this.
The engineers at Dell determined that the Receive-Side Scaling feature in Windows 2008 was not working reliably with embedded Broadcom NICs. It appeared to be driver related rather than a problem with Microsoft’s software.
We disabled the Receive-Side Scaling feature in the NIC and reliability was restored to the servers.