I've spoken heavily about this in previous threads, no idea which thread, but consider me the forum expert on this subject. This is a tech company model that others are starting to adopt and it is terrible, I personally hate it. Every company I've worked for in the last decade has had this policy... A few notes:
1) It is statistically proven that people take less time with unlimited days
2) No accrued time, so if you don't take as much vacation, it is a benefit for the company
3) On the flip side, if you abuse it, you'll hear about it
4) There is zero benefit to having "unlimited" days, I wish it was just illegal for a company to have this kind of policy. At the end of the day, it is just a way to screw the employee while looking like you care. Longer term employees get shafted bc they don't get any extra time for being at a company for a long time.