Pretty easy & smooth process to upgrade from VMware Infrastructure ESX 3.0.1 to VMware ESX 3.0.2. Since I'm running my systems off a SAN and using VMWare vmotion all I needed to do was put my first ESX server in maintenance mode and shut it down. This automatically moved all my running VM's via vmotion over to the other ESX server. I then put in the 3.0.2 install / upgrade CD and booted from it. CD Upgrade went pretty quickly, approx 10 minutes and then rebooted the system. After reboot my Virtual Center picked the system with no problems and I turned on a test machine to make sure it was working ok. I then moved over a couple production VM's without problems.
Since the upgrade appeared to work just fine I repeated the process on my second ESX server.