Pretty much useless. Pay varies so widely depending on state/city for example avg developer pay in San Francisco compared to Sacramento (100 miles away) fluctuates 10-15k (if not more). It also begs to question how honest people are when answering? Is this base salary or salary after benefits/bonus? As others mentioned, cost of living? San Francisco's avg 1 bedroom price is around $3120 while Sacramento is around $1000, that's $25,000/yr more in housing costs.
