Personally, I think that doing what you feel most comfortable doing is your best option, BUT contacting the hiring manger (or whoever did the interview in HR) is not inappropriate or unheard of. And is actually quite helpful if they are having a difficult time with the decision. By contacting them, you are expressing your continued interest in their company and, possibly, will even have another shot at extolling your virtues.

Did they tell you an approximate date that they hope to have a decision made? If they did not and your interview was a couple of weeks ago, go ahead and call. (Again, this is me personally, but if they don't give a decision date and you have forgotten to ask, then call one week and 1 1/2 days after the interview).

If they gave you a decision date, then call mid afternoon of the following day or the morning of the second day after the decision. Ie: if they said they hoped to have a decision by Tuesday, call Wednesday about 3:30. If they stated that a decision would be made by Friday, call Tuesday morning about 9:00.