I've started making vacation time a major part of the negotiation when taking a new position and in all instances I've brought it up during the interview process the interviewer acted alarmed. Even with my current position with a really cool small web shop they ended up interviewing me a 2nd time before offering the position. The key topic of conversation during the 2nd interview was basically the CEO trying to figure out if I planned on taking time off in some unspecified but inconvenient fashion that would leave the company in a bind.