A post on how to create a "no hypervisor" boot option using BCDedit. One of the first questions I got was whether this would allow you to use sleep / hibernate - and the answer was "no". Well, with Windows Server 2008 R2 the answer is now "yes".
So what does this mean? If you follow the directions in the original post you can have two boot options on your computer. One will allow you to boot Windows Server 2008 R2 with the hypervisor enabled (but no ability to sleep or hibernate the laptop), the other will allow you to boot Windows Server 2008 R2 without the hypervisor enabled (but you will be able to sleep / hibernate). This means that if you want to run Hyper-V on a laptop, you can set it up to sleep / hibernate while you are on the road / going from meeting to meeting - and still get full access to Hyper-V when you have wired power handy.