Note: Learned after this post that SLAT is only *required* for Client Hyper-V on Windows 8... not Server 2012. Awesome!
You may be running Hyper-V great on Windows Server 2008 R2 and want to upgrade to Server 2012, or maybe want some Hyper-V goodness in Windows 8 (finally!). But before you do, be sure your hardware can support it, because Hyper-V 3.0 has a new requirement of your processor for memory management.  Here's a great tip from Hanselman's Windows 8 power user post:
If you want, you can check your Windows 7 machine now and see if your system is 64-bit and supports SLAT and the newer CPU features you'll need. Download CoreInfo and from an Admin Command Prompt run "coreinfo -v." You want to see a start where it says "Supports SLAT."