I don't know too much about Glassdoor, but what I have seen from some of the other sites they tend to quote rates under the prevailing wages. When I was a exec, I had a hiring manager that reported to me, but all compensation was via HR oversight. They lived and died by one of the salary sites. For a particular position the site said that the market average was 75k. Everyone that came through the door wanted no less than 110k. The guys that had strong resumes where in the $150k range (this was a very specialized role). Because of those site under representing the market, My manager was unable to fill the roll so I asked for an increased budget and kept paying $300hr for a specialized consultant. Anyway, the point is I am leery of the salary sites after that experience.
Agreed - those sites tend to hurt the market when relied on like that - at the same time it would be interesting to see peoples honest salaries - perhaps without mentioning company names but instead just their primary roles or titles. This information can possibly prove to be useful much as the info from this thread has been useful to me.