I was happy to find an article talking a bit about
Hypervisor Security Concerns. It's not overly in-depth, but does point out the very real issue that virtualization poses some serious security concerns.
I think sometimes it's easy to get caught up in all the hype and forget about all the other issues a technology could create for us. I really like the title in the article
A New Definition of “Privilege Escalation”
Since it sounds cool, we should start calling a guest that breaks into the hypervisor,
Hyper Escalation. It both sounds cool, and is fun to say. (I have bolded, underlined, and italicized it to stress its coolness)
In all seriousness though, this is a good discussion point, and an issue that will likely continue to come up for many years to come. Virtualization, like many things to come before it, wasn't built with security in mind, so it's going to take many many years to hammer out all the dents.