I upgraded last week from WS7.1 to WS9. I'm running the same VMs that I was running before.
I have a dual monitor setup and I normally run one VM at a time in Full Screen mode, so it runs on both monitors.
With WS9, if I minimize the VM and leave it idle for a while (e.g. 20 minutes), the VM's screen saver/monitor off function kicks in - and even though WS9 is minimized, it actually turns off my second monitor screen (i.e. goes black, not actually power off).
If I click in the area of the second monitor quickly enough, some times it keeps it awake and starts showing the VM's screen on the second monitor, even though WS9 is still minimized and my primary monitor continues to show the Host OS.
If the second monitor does go to sleep, I click on WS9 in my task bar to restore it and it takes back over on my primary monitor, but my second monitor stays black and the only way I can bring it back to life it to click on the WS9 toolbar button to cycle monitors, so that I turn the second (virtual) monitor off and then back on.