I mentioned that there were a few dependencies around virtualized hosting which in my opinion are not that dramatic, unless of course you own a data center that needs to be refurbished...
Power is the biggie, with cooling right up there as well. Most cabinets/racks draw 4KW a rack (42U cabinet) if you through a loaded Blade rack in the data center, you are looking at 7KW, essentially double. So what, right?
You will need to have the ability to do high density hosting which means 200W a square foot vs. the standard 100W a square foot.
For cooling you will need/want special tiles in the floor that increase airflow around the cabinets. For safety's sake you'll probably want to drop another CRAC in for sites with seasonal spike in utilization and corresponding heat signature(s).
If you want a green angle on the cooling, look North my friends. The smart data centers are using mother nature's inherent cooling capabilities to keep gear cool. They shut down several CRACs and use an exchanger to draw very cold dry air into the facilities, reducing the carbon footprint of that data center through reductions in power usage and cooling.
Depending upon the age of data centers this will vary from extremely difficult/expensive/not worth it to a few weeks of refitting.