Consider what contemporary hardware could fit in as an affordable thin client. best I can come up with is either netbooks which are starting to cost under 400$ or maybe the most scaled down of desktops having say 512 MB RAM, 60 GB harddisks, but even these are not very cheap. Add to that full-blown operating systems like windows vista, which cost a bundle. The thin client cost can easily baloon upto 500$+ a piece. This can eat into the benefits of desktop virtualization. The OS problem is easily solved with linux, but hopefully in near future industry will make serious effort to provide scaled down thin client hardware which is very affordable (say under 100$)
If the thin client cost can be brought down, then the adoption of desktop virtualization will proportionally sky rocket.
The near future: Towards reducing the cost of thin client hardware most reports tell us that RAM, storage and chips are getting cheaper by the day and increasingly, the bottleneck in reducing cost for the thin client is the display technology. I dream of the day when, my laptop is as thin as can be and its LCD screen has been replaced by an small outlet for optical projection so that any flat surface can make do as a screen. Ah, but thats just wishful thinking for now...