A bit late on this post but time has not been available at the moment, however I thought this would be useful reading for you.
As hardware increases in scale, and new capabilities, such as Dynamic Memory, are introduced into Hyper-V R2 SP1, more and more customers are going to start to encroach on the supported limits of Hyper-V cluster nodes. As of May 2010, those supported limits stood at 64 VMs per cluster node, up to a total of 15+1 nodes, giving a total of 960 VMs. This contrasts considerably with the 384 VMs per non-clustered host, yet will still be more than enough headroom for most customers, however, in a recent announcement at TechEd 2010, Microsoft decided to increase the limits on the cluster nodes. The increase is actually pretty considerable too, helping customers to scale to much greater levels, especially on smaller clusters, assuming they have resource in their underlying hardware!
So, in a nutshell, Microsoft now support 1000 VMs per cluster, providing you don’t exceed the 384 VMs per node limit, which which will still be enforced.
Naturally many of you will be looking at this announcement and think, I am not going to hit those numbers but perhaps an area where you’re more likely to hit this limit, is when virtualising desktops, rather than servers. In most organisations, the number of desktops typically outweighs the number of servers, so hitting the previous limits was much more achievable, so this gives the organisation who happened to be creeping closer, a bit of breathing room.