[pixeloution]

Even if users were willing, this would be woefully inaccurate information. Mint shows take-home pay. But you have to keep in mind ...

  * People contribute between 0 to X% to a 401k. 
    This couldn't be deduced from take-home.
  * Many companies have a Employee Stock Purchase Program, 
    which is deducted from payroll.
  * Some (Many?) programmers get a large chunk of 
    compensation in options or RSUs.

I think self-reported is likely the only way to get numbers without some extremely invasive requests.