Most set-ups of virtualizing Oracle databases on VMware fail because storage I/O becomes a bottleneck. It turns out, 50% of all surveyed set-up had storage configured wrong. The problems has to do with storage queues in the VM and subsequently on the ESX host. Additionally, vSphere 4.1 introduces features (SIOC) to optimize the I/O better to the SAN and para virtualized SAN drivers can further reduce latency and increase throughput.
Then the webcast also mentions Oracle's "native" NFS client (dNFS, PDF) inside the database kernel. This reduces the CPU overhead and latency normally observed on NFS client in the OS. By using Oracle's native NFS client, you can use shared storage in a grid computing environment more easily and the same way on Windows as well as Linux.
EMC VMAX SAN box has a feature called FAST VP which can optimize and distribute your storage needs from all-SAN to a mix of SSD, SATA and SAN where and when needed.
Very interesting read and much stuff to think about your own VMware set-up when using Oracle software.