I'm having issues with my NIC's losing network connectivity. I've tried using vmxnet/enhancedvmxnet/flexible, and still having issues. I also have strange timeouts on my ESX hosts. I had to manually load vc agents on some hosts, and update manager would timeout in the middle of updates on others. In some cases, ESX servers will reboot and come back up, and are pingable, but they won't register with VC, unless I disconnect/reconnect. Very odd behavior, and I'm thinking it's related to some security features on the switches, but I'm not familiar enough with them to be sure.
I haven't been able to find any docs with interoperability with vmware or best practices.
VMware vExpert 2009