Totally agreed. Are you serious about letting people take vacation? Give 6 weeks paid vacation per year. It's not that hard: six weeks is more than "unlimited" would practically turn out to be, and it's well-defined enough that there's no guilt or anxiety about whether someone's abusing the privilege, and it's low enough that you get roughly a year's work out of the person anyway.
I used to work at a company with unlimited vacation and I definitely didn't take a lot of vacation, but what I most appreciated about it was not having to sit there and figure out how much time I was taking off. If I had to be out for an afternoon(or just part of the afternoon), I never thought about whether I was taking a half day of PTO or not, I would just let my team know and go. That's the freedom I appreciated much more than the actual amount of time I took off. I think this blog post was definitely getting at this when they were talking about going from having control over your schedule to going to kindergarten. Where I work now is pretty relaxed about needing to take a couple hours off to run an errand or working from home, but it's still definitely something I need to think about.