I like and follow Dave's advice. When im at work, I work hard and get done what I need to get done. When its time for a vacation, i take it. I leave work behind, projects completed or not. I forget about work and concentrate on vacationing. I always give my boss at least several weeks notice of my intent to take a vacation so he can be aware and make any necessary personnel changes to keep the workflow going if there are any conflicts. In my field it is very easy to get burnt out and we all realize there are times where you just HAVE to get away for a bit. Thats all there is to it.

Looking forward to this!