From the 18Jan2010 article "Emerging Ethernet standards could reduce complexity in data centers" from Network World -
"The emerging standards would offload significant amounts of policy, security, and management processing from virtual switches on network interfaces cards (NIC) and blade servers and put it back into physical Ethernet switches connecting storage and compute resources."
One of my first questions when working with virtualization software had to do with the above. If you are running 10 virtual machines off of one physical server, then the NIC (or multiple NICs) on that server is also working as a virtual switch - this means lots of extra work. The emerging IEEE 802.1Wbg and 802.1Qbh standards will help. Interesting stuff if you are an uber geek.