How long would you sit and wait?

As long as I need to... but I would judge them poorly as employers and might opt out.

It's very disrespectful.

I would wait the length of time they scheduled me for the interview. If it was an hour interview, I would excuse myself once the hour was up, let them know I would be happy to return, but that my next interview, with their competitor, is already scheduled, and I don't want to keep them waiting.

20 minutes. This is your time too. If they can't respect that, they won't respect you as an employer either.

Also, I would think it was a test to see my reaction to the situation.

Nik nailed it.
well played.
whether theres another interview or not.

In a half an hour I would see if I could find a receptionist or someone else to see if everything was ok. All up I would wait just over an hour then leave a message with someone and leave. Stay any longer you might look like a desperate person with no back bone, guess it all depends on what type of work it is.

Until retirement I was an senior aerospace quality engineer, any firm that behaves in such a manner is not into quality.

Probably after about 12-15 minutes I'd step out and ask if everything was all right. I wouldn't complain, just find out what's going on.

Professionalism is a two way street. There is talk about how to conduct yourself in a workplace, but one expects the bosses to be professional as well.

Therefore, if it takes more than oh, 10 minutes, open the door and yell for the interviewer to get her god damn tub of lard worthless fucking ass in there to do the interview.

When she comes back, tell her that stuffing her face with candy and playing on sites like IIN is going to have to wait til she gets home to her cheating husband and snot-nose pesky brat kids.

As long as needed. It's her office so she will have to come back at some point.

This was some shitty " test" some companies do...i dont play mental games.
I would wait maybe 15-20 minutes, then find someone and ask where is the interviewer?? If nobody showed up, bye.
My time is not to be wasted. I dont appreciate playing mind games.

I'd wait until they called me even if it's a few hours of waiting time. I figure I came there, I may as well see it through. Though I wouldn't take the job if they hired me since waiting long would be an indicator of a terrible workplace. XD

As long as needed, I bring a book with me anyways.

An hour. Any longer than that and I would think she had just completely forgotten.