BrianMadden.com recently posted a great article on the upcoming feature of Dynamic Memory for Windows 2008 R2 Service Pack 1. The article focuses particularly on the impact for Virtual Desktop Infrastructure (VDI) deployments. For both reasons I recommend taking a moment to read the post. You may find yourself adopting SP1 sooner than you expected.
A closer look at the new "Dynamic Memory" feature of Hyper-V: is it worth it for VDI?