The problem I'm already seeing with virtualised desktops is that they're locking in at a generation behind - i.e. today we have IE9 shipping with GPU acceleration, and my MD already questions why our virtualised desktops don't look like the Aero theme he's familiar with from his local desktop, why fonts don't look as good, why Flash apps don't work as well - and can we do something about it?
Well, technically, yes, but not without giving up a lot of the cost savings of virtualisation - i.e. our virtual desktops don't have GPUs, and we use a low bandwidth model as the main thing is supporting remote workers. I know it's possible to virtualise a high-end graphics workstation, but most of the large projects I know of, tend to be aiming at a low-end spec - they are virtualising existing needs.
The big question for me is what happens as web apps become 'richer' and more dependent on a client having some grunt. And by grunt, I mean the amount of grunt available on a moderate Android phone. Will virtualised desktops be the new green-screen terminals?