Ahhh, unlimited vacation. The new notion that sounds wonderful, yet ends up being the epitome of crony capitialism policy. It's a growing trend in corporate business, and it definitely benefits the company, not the employee. Without policy guidance granting time/days, every time you request vacation can be used against you (like in this strip), and without guidance employees tend to take much less actual vacation than if they had given days that they can take. Those who do benefit are the most Sr. Managers and their toadies.
Thankfully living in the UK, there is a minimum work entitlement for full time employees of 28 days paid holiday, tho due to work benefits I get slightly more than that. That said companies in the UK are able to mandate that 8 of those days to specific days.