For all those who are interested in NVGRE network virtualization that come with Hyper-V 3.0 I suggest to take a look at articles:

http://blog.ioshints.info/2012/12/hyper-v-network-virtualization-wnvnvgre.html

http://blog.ioshints.info/2011/09/nvgre-because-one-standard-just-wouldnt.html

And there are alot of questions about NVGRE gateway here is one vendor that is working on it:

http://www.nappliance.com/

http://www.nappliance.com/windowsserver2012