Hi Tom,
I found some decent documentation on each of the vSphere VAAI 4.1 primatives and what they do. Here's the explanation:
Block zeroing (WRITE SAME)
When creating a new virtual disk (VMDK) in the ESX server, areas are zeroed out. By off-loading
the processing to the disk arrays, the resource consumption in the ESX host can be reduced. In
addition, because only control instructions can be exchanged between the ESX host and the disk
arrays, traffic on the storage network can be reduced.
Full copy (XCOPY)
Copy processing, such as creating a clone of a virtual machine, is off-loaded to the disk array.
Because the ESX host does not have to read/write data when copying it, the ESX host workload
can be reduced, and traffic between the ESX host and the disk array can be reduced, resulting in
improved copy performance.
Hardware assisted locking (ATS)
The function that locks volumes when updating VMFS metadata is off-loaded to the disk arrays. By
enabling exclusive lock per block with the lock mechanism of the disk arrays, SCSI reserve command
contention can be reduced, and this leads to improvement of VMFS scalability.
VAAI is for more than accelerating vMotion and hopefully this helps a bit. I'm sure there's more detailed descriptions out there but this might help you decide if you should look more closely at VAAI. I'm also guessing that there will be more primatives added in the next version of vSphere but we'll have to wait until next week to hear about those.