I came across this article and a few others linked to it this morning and taught it was worth sharing out

here is the link http://blogs.msdn.com/b/rds/archive/2010/10/15/remote-desktop-connection-broker-scalability-testing-results.aspx

this particular one is about scalability but there is links for capacity planning

load simulation and running it as a virtual machine!

i think if your thinking of doing VDI and its not a complex infrastructure then pure RDS is worth investing time in, if it is a large scale project then you need to compliment rds with Citrix Smile