Just released on the VMware Flings site is a fling which is designed to help when you make the move from ESX to ESXi, this tool will help you check hardware software and also that there are no lingering scripts or locally stored VMs etc.

A great tool to download and run against your environment to ensure you have caught everything before the move to the next version of ESXi.

--> Please see the rest on the website :

http://www.virtu-al.net/2011/12/01/migrating-esx-to-esxi/