I've used both DSS v5 and v6 (now in SCST mode) with Autofailover and vSphere 4.0. I'm using Jumbo frames and File I/O mode in DSS. There are some tweaks posted in this thread that fellow forum members have recommended; your mileage may vary.

My recommendation is to make sure that you pay attention to your physical i/o characteristics. One thing that surprised me was that your write speeds will be dramatically lower with autofailover than without, because with synchronous replication your write cache should be OFF, and this reduces the speed of write i/o to the speed at which the disks can handle it.

Also, make sure you have a maintenance window during which you can shut down ALL of your VM's if you ever need to do software updates on the DSS or add volumes. You can't do that without stopping the autofailover service, which stops iSCSI, which means your VM's don't see their storage anymore

Finally, remember that DSS is just software. It's well-designed software but you have to have reliable hardware to go along with it if you are going to rely on it for production use. There's a reason why EMC and HP and Netapp cost a lot - it's the software and the hardware. You can get into a SAN for a lot less with open-e but if you put low-end hardware in your SAN, you'll get an unstable system.

Just my few thoughts...