See also the link to event Id 27 from e1kexpress.
We thoroughly researched this issue and it appears to be related to specific intel drivers on the 8000 series NIC's. This will affect many PC's and windows update has recently set a driver to recommended download that will cause this problem to occur. Take note that it is a "SIPS" problem and can be reconfigured to resolve the problem. Otherwise a driver update directly from Intel's website to latest version (11.5 as of Sept. 2010) will fix it as well.
If you are noticing a consisten drop of your connection with an 8000 series NIC from Intel update driver and don't allow MS update to give you this bad version.
I had problem with two DELL OptiPlex 755 with Intel 82566DM GB cards, loosing connection to network every so often for about 2 seconds. Dell knows this was an issue and have put a fix in a BIOS update (A10). Load new BIOS.