I've written quite a bit in the past that VDI is about not about making your desktops easier to manage—it's really nothing more than a form factor change that delivers some new capabilities. In our book The VDI Delusion, we talk about how the #1 reason that VDI projects fail is because companies try to do too much at once—and desktop management is a big part of that "too much."
For example, a lot of people buy off on the idea of VDI because it's "easier to manage." They hear about the disk image sharing or cloning or whatever, and they think, "Heck yeah! Managing one disk image is easier than managing hundreds!" And while I won't argue with that, I will point out that you can only actually manage one disk image if you can implement app virtualization, user state virtualization, and a whole host of other desktop environment delivery components. (Of course this is also assuming that all your apps are compatible with app virt, that no users want user-installed or departmental-installed unsupported apps, etc.)
I don't write this to scare off anyone who's thinking about VDI, rather, I just want to point out that if your current desktop environment is one where every user has his or her own unique disk image, and your plan for VDI is that you're going to move to a structured shared image model… you're in for big pain! In fact moving from the personal to shared disk is much harder than the actual VDI technologies.
With shared-image VDI (or any shared-image desktop virtualization), your users are starting off with a gold master image that you customize on demand with application & user virtualization. If that sounds appealing to you, then I have to ask: why aren't you doing this today? If your environment is ready for central image management, why haven't you been using Ghost and SMS and automated app installation for the past twenty years?
If your current desktop environment is physical PCs and laptops that each have their own images with locally-installed applications and you want to move to VDI with shared images—you need to stop right now and create two projects that are unrelated to each other.
One option is to forget VDI and focus on your Windows client management. Think about things like SCCM, Altiris, app virtualization, and user virtualization. Get those all built-out for your physical environment. Only once that's done and successful should you think about VDI.
Or, if you really need the benefits of VDI today, then forget the shared image thing for now. Just recreate your current 1-to-1 persistent image desktop model in your VDI environment. Once that's all up and running you can start to sprinkle in application or user virtualization.
Bottom line: I can't tell you how many people I hear who want to implement shared-image VDI. Then I ask them if they use something like Ghost to re-image their users' machines on a daily basis in their current environment. Usually they say, "no," which leads to me asking why. They say something about how unique their users are or how they have complex apps, and that leads to, "Well, if you haven't figured out how to do this with your physical desktops today, how do you magically think it's going to work in your VDI environment tomorrow?"