I work at a major retailer who recently adopted this vacation policy for certain upper levels of management. I suspect that soon the policy will roll out to all salary folks. Let's face it, this policy is a shrewd but effective business move.
The company gets to paint it as wide open unlimited vacation. The truth is that people take less vacation because of peer competition and manager approval or pressure to be at work. HR is NOT in the business of making things awesome for the workers, whether salary or hourly. Labor is like equipment. HR wants to buy the best performing equipment for the lowest price, or lowest cost of ownership. But they don't want to say that.
Unlimited vacation looks and sounds great. But the reality is they hope to lower the cost of ownership for the equipment, us. If a piece of equipment acts up or doesn't function well, or performs when you need it, what do you do? You replace it with a newer cheaper version that will do what you need it to, and you do what you can to lower your TCO or total cost of ownership.