The OVF will be updated infrequently — there is a software package you upload in a management interface that installs the new software and configures your instance with the updates. It's pretty seamless — download a file, upload it, wait a few minutes for install and you've got an updated version of GitHub Enterprise.
Lots of FUD coming from the community- at first glance it sounds bad, but a lot of us should do the math before getting the pitchfork ready. ( Script to help "do the math" http://www.lucd.info/2011/07/13/query-vram/ )
We will actually be saving money with the vRAM licensing changes.
It looks like by changing the pricing to reflect more of the provisioning they're encouraging people to stick more CPUs per guest. I guess the more people are overloading their hardware at the moment, the bigger the license price jump.
[0] http://www.clickstudios.com.au/