Seems that vmware has released an ESX version ( 3.5 Update 2) that can stop working after August 12.
“An issue has been uncovered with ESX/ESXi 3.5 Update 2 that causes the product license to expire on August 12. VMware will reissue the binaries in the next 36 hours (by August 13, PST). Until the issue is resolved, we advise against upgrading to ESX/ESXi 3.5 Update 2.”
Should be interesting to follow.