So I've (just like most other VS/TFS geeks) downloaded the latest bits to try it out. Apart from the expected wait-for-download the many-GB-files the setup went great. VS 2008 setup took about an hour to complete and installing a new TFS 2008 from a bare Window 2003 Server took less than two hours. Since the installation of TFS nowdays is a pretty straight-forward procedure I wasn't expecting any trouble so it was good that the new setup worked flawlessly.
Since most people only can access the 90-days trial you can still upgrade using the trial versions. When you have the right keys all that needs to be done is to re-run the setup and in the options you get it's possilble to enter the new license key to activate the product.
Next up is to upgrade our internal TFS 2005 installation to 2008. I think it will be a bit more challenging