I disagree about the limits, but I do agree that it will take another three to five years to complete the cycle of baseline development around virtualization standards. As with all "Intel" based solutions, as mentioned in the article, there is a competition that both helps and hinders true growth of the technology.
With it's infancy in the data center, there is also the question of long term management and support of the virtual environment. Anyone can put it in, but with the proper "4 P's" (planning, policies, processes, and procedures), then you will find that you quickly reach the limits of the environment, and your staff.

Click to read the article this is in response to.