FreeBSD having two iSCSI targets and an initiator, and VMWare in the latest edition having access to the three probably most used remote storage technologies - iSCSI, FC and NFS - there is room to play the combinations and see what is best and most convenient.
Sometimes, when things go right, they are really beautiful to watch. Like adding a virtual (SCSI) drive to a running virtual machine freshly copied from ESXi 3.5 to vSphere 4, seeing that drive simply appear in the guest system in a hot-plug fashion, creating a ZFS pool on it and watching iostat as data is migrated from the old drive which has gotten to be too small (and uses UFS), to the new one on which the magic of ZFS will allow the file system to grow indefinitely (as the damn application is greedy in a stupid way), and seeing that "pausing" problems ZFS caused on ESXi 3.5 really are solved in 4.
I finally have a VMWare ESX 4 (vSphere 4) in production and it's time to see how much we lost this time in the name of greater flexibility. In short: the usual (which is a lot).
VMWare ESXi is a great free-as-in-beer product bringing professional virtualization within everyone's grasp. Contrasted to VMWare Server 2, I'm yet to find something really serious in ESXi, to rant about, but the lack of software RAID support comes very near. For some strange reason ESXi doesn't support software RAID configurations (officially it's all about "reliability" but I suspect they're either not interested in building management products for sw RAID into the various management "consoles", because sw RAID appears to be at the low end of the market or it's something to do with the ESX's dubious interaction with the GPL).