One big thing about Exchange or SQL under VMware would be to correctly align the disk. improperly aligned VMDK's don't make themselves apparent on web servers and other low task servers, but when you load SQL or Exchange or other database applications performance issues are more apparent.
Netapp best practices the starting offset must be divisible by 4096. The recommended offset offset value is 32768. You can find this information by running msinfo within your VM and looking at the Storage>Disk>Partition Starting Offset. usually you will se a VM setting of 32256 which is incorrect.
information on correcting the offset and improving performance on Netapp based storage systems can be found in this PDF.
Good call Dave. LUN alignment in general (physical or virtual servers) is definitely key for performance in an Exchange or SQL environment. If you use SnapDrive (5.0 and later...supported on ESX), it will properly align any LUNs it creates.