I've ran into this a few times here and each time I stare at my screen for some time (depends on how much coffee I've had) and then remember this change. When you install Vista SP1 or install Win2k8 the console switch for MSTSC will be ignored (it's gone). They've made a change that requires the use of the /admin switch now. So if you want to connect the console on a Win2k3 server then instead of using MSTSC /console /v:<servername> now use MSTSC /admin /v:servername.
Why the change? Check Nick's post for further details and a link to the TS team blog with more info.
The more you know...
Here is the TS teams blog post with all the details you'd ever want to know: http://blogs.msdn.com/ts/archive/2007/12/17/changes-to-remote-administration-in-windows-server-2008.aspx