I have seen as fast as a week and as long as 4 months. They do not do a very good job of letting you know what is going on with your employment until the last second. Eric G. is paranoid that he will get sued if he even hints a job offer and then does differently. So my advise is to be patient and call everyday! If you felt the interview went ok then all is well. Getting the interview is 90% of the battle.
Back when I was hired, job offers were made either at the interview or within 48 hours generally. My position was offered immediately after the interview. I have spoken with people in the past year or so that have received offers at the end of the interview, and others that have not received them for a few weeks. I wouldn't suggest calling every day, but twice a week would be acceptable as far as I am concerned.