I also tested a setup with running VirtualBox (Vista as guest, 8.1 as host), and I experience no issues like you mentioned. However a couple of things you can do and assuming you setup your plugins (with only the Java ME 8 plugin) as described in the course:
1) Increase number of CPU (between 2 - 4 cores) and RAM to 4GB in VirtualBox
2) If you encounter the hang again, don't uninstall Netbeans, rather run Netbeans using a clean user directory and see if it still hangs. See this article on how to do this.
3) If after done (2) it still hangs, the problem has nothing related to Netbeans or plugins since you started Netbeans in a clean state (without any plugins). Perhaps the problem could be hardware related such as a possible bad disk or RAM. If not hardware, then software such as VirtualBox running host OSX could be an issue (not sure though).
4) If after done (2) it does not hang, then there might be an issue with the Java ME 8 plugin running in such an environment like you described or something relating to your setup.
I tried installing NetBeans in a VM and it hangs routinely. My VM is a Hyper-V installation running Windows 8.1 with 8Gb RAM and 80 Gb of drive space allocated. NetBeans ran just fine until I installed the plugins required for the course. Then it started hanging. I have multiple desktops available to me so I did a clean install on a non-virtual machine and it worked just fine. I haven't had a lot of time to research the issue, so I am following this thread with interest.
I essentially follow step 2 these days by deleting the user directory and restarting and reconfiguring Netbeans. So I'm pointing my finger at the Java ME 8 plugins . I've followed your advice with respect to the number of cpu's and memory, and I'm also now following a policy of explicitly shutting everything down in reverse order to that in which I started them. So first I halt the Raspberry Pi, then remove it on the Device Connections Manager, then finally close NetBeans down. Since I've done this I've not experienced problems so far. Touch wood...
Thanks for the advice
You're welcome Martin, I never thought about shutting sequence being a cause of concern. Come to think of it, my shutting down sequence is similar: Shutdown the Java ME AMS, and you will notice the Java ME device manager will automatically disconnect from the RPi, then I close Netbeans. Thereafter, I shutdown the RPi.
I wish you success!