Often while interviewing, the hiring manager already knows who exactly they are looking for. While often the qualifications on the resume have a lot to do with this, so does the overall interaction and personality of the person who is being interviewed.
My largest issue with interviews is not knowing how I did or where to improve. While I can't say that I have interviewed hundreds of times to know if my techniques work or not, I've had enough to know that I either I am doing something wrong or I am simply not desireable. Well, I hardly think it is the last. I think that employers are often intimidated that I have dreams of persuing much greater things such as my masters, a law degree, and my CPA among other things. I simply am too ambitious for the positions that I am applying for. However, that doesn't mean that I don't need it. I need the experience and the backing of a company, the guidance and mentoring that they can provide. If provided, I couldn't very well just leave them in the dust!
Anyways back to interviewing, as I said it is very difficult to know how well you did during the interview. Much less where you can improve unless you wish to pay for services that simulate the interviewing process. Those can be very costly, and may or may not relate to the interview that you may be in.
I fully believe that a new system should be developed that would allow employers to give a basic rating system for those that they interview. Through a very basic site, which hopeful candidates enroll in at no fee, employers can log on and rate the candidate through set options (otherwise liability and defemation of character suits would prevail) that would take no more than 2 to 3 minutes at the most. Obviously, this system would not provide full details but such things as did you present yourself well, did you speak well, did you identify your strengths and weaknesses, and did you show actual honest interest in the position and the company. It would be educational! Obviously, employers are very busy at this time with so many candidates as the country is facing unprecendented unemployment, I think that this would go further to assist those of us looking for positions to hone our skills and communications. Maybe we would back off on applying for jobs that we really don't want and that we aren't qualified for. I would simply like more feedback! What am I doing wrong? What am I doing right? Am I doing anything right??? I would imagine that alot of people could benefit from such a system.