This is just a quick note on a problem I've just experienced (and found a fix for!).
Having just built a new Windows 2008 VM and mounting the ISO from my NFS ISO datastore, I was surprised to see that the actual install was crawling along very slowly at the "Expanding Windows files" section:
As the above link indicates, the problem was the ESX hosts NIC configuration. Set to "auto-negotiate" (which it should be on gigabit connections), the port had managed to negotiate down to 10Mb half-duplex(!). I changed this to 1000Mbit full-duplex and then back to auto-negotiate (where it stayed at 1000Mbit full-duplex).
And the performance became speedy again!