At some time during the TechEd 2010 conference Microsoft made a significant change in its configuration limits for Hyper-V.
While the previous supported limited for a a single Hyper-V host in a fail-over cluster was of 64 virtual machines, this number has been increased to 384 virtual machines per host.
The total number of hosts allowed per cluster remains equal to 16, with a maximum of 1,000 virtual machines across all nodes.
As the support article confirms, the change applies to the existing version of Hyper-V R2 shipping with Windows Server 2008 R2 and not to the upcoming Service Pack 1 that will be released later this year
Thanks to ServerTalk for the news.