A guaranteed amount of time off means the company has to pay me for unused vacation if and when I depart. So for those of you who are offered unlimited time off, get a guaranteed and generous minimum, in writing.
After all, if it's unlimited, they shouldn't mind putting "a minimum of four weeks a year" in writing, should they? If they won't, they're probably going to shame you into working all the time and then won't pay you for the vacation you didn't take.