I think you should follow up after a week. If you do follow up, follow up in the least intrusive way first. Get more intrusive if you don't hear anything. In other words, start by emailing. If you get no response, try calling. If still no response, follow up in person. If you have followed up and made contact once and they give you a give it another 1 and 1/2 to 2 weeks to follow up again.
Unfortunately many employers don't bother getting back to you unless they are interested. And even if they are, circumstances may be such that they cannot make a decision - such as vacations. If they told you in the interview that they will be making a decision in a week, it is perfectly OK to call after 8 days, saying "I'm following up, since you mentioned a week.Do you have any questions that I can clarify?"