I lose, so customers win!
I made a failed attempt to see if we would be willing to make the next version of Team Foundation Server only supported on Windows Server 2008. Since we'd like to have native IIS7 support in our setup (not require the IIS6 compat like we do in TFS 2008), we're looking at maintaining 2 different code paths, the 2k3/IIS6 method (already coded and tested, thankfully) and the new IIS7 code.
There ended up being a whole slew of benefits to being Longhorn-only (much smaller test matrix, ability to take dependencies on some IIS7 features, powershell in the OS, etc), but it's not going to happen, at least not for this release.
This means our job is a bit tougher, but for all of you playing along at home, be happy knowing that (at least as things stand now) we won't be forcing an OS upgrade with our next version of TFS :)