I like this idea of minimum vacation. Most companies I've worked in use vacation days as some sort of reward for sticking with the company for X number of years (i.e., "When you hit your 5 year anniversary, you get an extra 1.5 days of paid vacation. Won't that be nice!"). And when I say paid vacation, I really mean PTO with no separate 'sick leave' days. Which means people show up to work sick.
Funny enough, the company I work for was recently bought, and in the interests of making things 'uniform', we were forced to adopt the purchasing company's vacation policy, which meant an across the board cut in everyone's PTO hours (to include folks that negotiated additional vacation days when they were hired -- those agreements were declared null and void). Apparently the execs thought the hit to morale/retention was worth the 'cost savings'.
On the other hand, I once interviewed at a company with an 'open' vacation policy and was immediately suspicious of it. My first thought was "I'm guessing people don't take much vacation?" That didn't go over so well with the interviewer.
It's nice to see an employer that treats vacation as a means to increase employee productivity and retention (burnout prevention, etc.), rather than as a pure cost to be minimized as much as possible.