Without a paid license, you can no longer add a virtual hard disk to a running virtual machine on ESXi 4.0.

You are prompted with an error message about not having the &quot;licensed feature&quot;-- after doing some research online, there are some who believe it's a bug, but others who point out that &quot;Hot Plug&quot; now requires a license, and works while running the 60 day feature-rich evaluation.

Definitely something to be aware of if you plan on running standalone ESXi servers in your environment-- caused me some grief when trying to get an Exchange server up and running.