Tim,

Chin up.
If they were trying to nudge you they would have told you that the position had been filled.

Maybe they haven't separated the wheat from the chaff yet.

It is hard to hold back making that return call, it is like when you are given a hot girls number you just feel the need to call now. I figure the middle of the week I should call. I am hoping that with it being a Friday they wanted to just get out of the office and on with their weekend.

So, in your phone call bring your concern to the table. Tell the person you realize they are very busy and you don't want to contact them at an inappropriate time. Ask them when you should call back. Most people react quite favorably to that and will be frank with you. (ie - I can't believe how swamped I am. The stack of call backs are under this and this project. I will get to them next Monday) And then, call whatever day they say.