Interesting info about storage performance in article 'What’s New in VMware vSphere 4'
Pages 5 and 6 are filled with very interesting info about "VMware Paravirtualized SCSI (PVSCSI) Emulated versions of hardware storage adapters."
I look forward to testing this out, particularly under the next version of ESXi, although the default SCSI driver in ESXi 4.1U1 seems to have excellent speed already.
May 26 2021 Update
An archive of how the original article appeared is in the Internet Archive WaybackMachine here.
The link above is no longer available, but the PDF has been located here.