Sure - we have no fixed vacation policy (apart from that fact that it's unlimited). It's purely based on mutual respect. If a team-member wants to take vacation, its up to him to be responsible and plan accordingly, make sure projects are finished etc. Of course, respect means that you shouldn't take 6 months off. But to date we've never had an issue and we've been doing this for two years and will be close to 20 people soon!