VMware is telling me this may be a known issue: http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2073390
Do you have sparse disks (space reclamation) enabled? I do on my new pool where the hung VM from Wednesday lives, but I just don't remember if it was on for the pool where the first VM hung. I suspect it was though as it defaults to being on when you create a pool.
Geoff