Until I left the US every I worked operated on the basis of accrued vacation. The day you started you had 0 vacation days, after 6 months you could use half your annual allotment, etc.
My current company does this. In addition balances have to be used by the end of the year. People are encouraged to take their vacation, so this leads to a lot of people taking random days in December off. As a result you can't get a damn thing done in December.
I can't help but think that a system where accrued days expire after a certain amount of time or you can't carry more than a certain balance would mean that people's vacation time would be spread out more. As a result I could actually get some stuff done now that requires coordinating with people. I'm not sure if there would be a cost, however, in not being able to get stuff done at other times of the year.
