As you already know, the product group announced the Dynamic Memory feature for Hyper-V with the SP1 release. Here you will find several links with information about how the new functionality works.
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
How do you manage dynamic memory from Windows 7?
What is "memory priority" when service pack 1 is installed?
What is the memory buffer when dynamic memory is enabled?
What happens if you enable dynamic memory on an unsupported guest operating system?
Enabling Dynamic Memory