Definitely still different block sizes. I've gone into the properties for the different LUNs, and I can see some at 1, 2, 4, and 8 MB. I think the change to new storage happened before the 5.0 upgrade, too, so the LUNs are new-ish, but were created back in our 4.1 days.
I'm 99% sure VMware knew I wanted thin provisioning. I was in the advanced options window (multiple disks on the server, only moving one at a time) and left it at the default "same format as source" setting in the storage vmotion wizard. I'll try again, manually specifying thing provisioning, just in case that part has gone haywire.
