I have just found out a GREAT new feature included in Windows 7 / Windows Server 2008 R2 :
Multiple monitor support for Remote Desktop Services allows users to open a Remote Desktop connection expanded across all the monitors on the client computer regardless of the client monitor configuration. With this feature, the user can fully utilize all the monitors connected to the client computer for the Remote Desktop connection thereby providing extra desktop space and an almost seamless experience with the client desktop that is much improved over “Span mode”.
I have been so frustated so far to not be able to fully take advantage of my two screens in remote scenarios. And it is more and more usual to work on virtual machines. For instance I develop with Visual Studio 2010 on a virtual Windows Server 2008 machine, and I was not able so far to fully utilize the multiple screens support of VS2010. I now can:)
The only thing to do to initiate a remote session with multiple screen support is to check the "Use all my monitors for the remote session" box: