Have a host that refuses to remediate updates. In the /var/log/esxupdate.log is this error message.
2012-03-25T00:53:30Z esxupdate: HostImage: DEBUG: Live image has been updated but /altbootbank image has not. This means a reboot is not safe.
I've had similar issues where I've had to reboot, sometimes twice to get back into the pre-update stage, and have had to run through the update again.
Called support and found that one of the guests had a stuck vm tools install which did pass must when trying to migrate all the machines off. Ended the install and everything went well from there.