Unlimited Vacations. Too much of a good thing?

At first glance it sounds like the coolest thing ever -- you’re going to work for a company that offers an unlimited vacation policy. That’s right, unlimited, as in, take whatever time you need. This is catching on in Silicon Valley, especially among smaller, younger companies. My current employer, a 500-person software company, offers unlimited vacation, as did my previous employer, another internet company of about the same size.