My colleague Kathy Davies has published a quick demo of DM in the SP1 Beta on YT:

Principal PM Vijay Tewari also showed DM, and Remote FX (both available in the SP1 Beta) at TechEd2010:

The product group has the definitive series of blog posts on Dynamic Memory, now available in Windows Server 2008 R2 SP1 Beta

Part 1: Dynamic Memory announcement. This blog announces the new Hyper-V Dynamic Memory in Hyper-V R2 SP1, including requirements. http://blogs.technet.com/virtualization/archive/2010/03/18/dynamic-memory-coming-to-hyper-v.aspx

Part 2: Capacity Planning from a Memory Standpoint. Details issues to consider for memory capacity planning and why. http://blogs.technet.com/virtualization/archive/2010/03/25/dynamic-memory-coming-to-hyper-v-part-2.aspx

Part 3: Page Sharing. Detailed discussion about the TLB, large memory pages, how page sharing works, SuperFetch and more. http://blogs.technet.com/virtualization/archive/2010/04/07/dynamic-memory-coming-to-hyper-v-part-3.aspx

Part 4: Page Sharing Follow-Up. Questions answered about Page Sharing and ASLR and other factors. http://blogs.technet.com/b/virtualization/archive/2010/04/21/dynamic-memory-coming-to-hyper-v-part-4.aspx

Part 5: Second Level Paging. Details why should avoid this in a virtualized environment, including Performance impacts. http://blogs.technet.com/b/virtualization/archive/2010/05/20/dynamic-memory-coming-to-hyper-v-part-5.aspx

Part 6: Hyper-V Dynamic Memory. Discusses DM, and each of the per virtual machine settings. http://blogs.technet.com/b/virtualization/archive/2010/07/12/dynamic-memory-coming-to-hyper-v-part-6.aspx