We actually suspect that people who are paid less or are underpaid are more likely to report their salaries. For example, it seems like Glassdoor data skews low.
IMO sharing salary data is the perfect first step for some sort of software engineers association/guild/professional body.
And perhaps more relevant to the thread, I know two types of people who talk about their salary, people who make a lot and people who make a little. Their is just so much bias present to me to give any credibility to these lists. Take the google spreadsheet where the employee was fired, do you think the engineers who thought they did better then their peers in negotiations listed their wages?
At it's simplest level I think something like the SAG or profession sports players associations. Kept out of the way, stars can rise, and there if you need them. It'd be useful to be able to have an organization that I can say "Hey, I'm interviewing at Github, based on your verified compensation data that you keep, what can I expect?"
The fact is, our employers share and buy each others compensation data similarly for use in negotiations and when setting compensation. It only makes sense that the parties on the other side of the table do the same thing.
Surely scalping a ton of mid level engineers at major tech firms for sharing their salaries online will fix that pesky problem of soaring profits and thick margins...
There is a market for doing user submitted comp analysis, but the real value is building trust, which takes a very long time and is expensive.