<posh_Voice> It's all about the Dynamic Kernel Address Space, don't you know? </posh_Voice>
Read all about it here: http://www.thincomputing.net/articles/one-reason-why-windows-server-2008-terminal-server-will-allow-you-to-get-more-users-on-2.html
Great Article by Michael Roth - Definitely worth a read.
He's also got some interesting articles on the Terminal Services 2008 Architecture, Parallel Session Creation and Session Broker.
Looks like TS in 2008 is pretty good! :-)
One of the things that more and more people I speak to, find really interesting in Terminal Services