Even though I didn't have a very challenging topic (Installing Multiple OS), it was very difficult to prepare enough to make sure that I could explain the topic to other students. It took me about 2 hours to prepare for the lab session (I didn't attend the training session), but I didn't know that we weren't going to cover all the methods of installation.
The lab session turned to be surprisingly easy to handle. The teaching assistants occassionally gave some input to us about how we should handle the class. The class didn't misbehave much (mainly because they were afraid of us giving them a bad evaluation when it was their turn to lead :P), and the lab session went along smoothly.
It was great using QEMU and VirtualBox, but I found myself wishing that we could use VMWare Player too. It would also have been nice to have been able to install a version of Windows as a virtual machine.
Personally, I thought that Lab Session 3 was one of the most useful lab sessions because almost everyone used the knowledge they gained during the session later, installing a Linux - based operating system.