Glassdoor, public salaries and does that add up?

I have become intrigued by glassdoor.com and I am not the only one I should imagine. It aims to help demystify salaries and employee opinion by gathering mass contributions in a web2.0 ugc style.
Clearly this taps into the whole trend for sharing, and one that I am usually quite happy to go along with. Indeed I think that openess in organization atleast on salary when performance is said to be relative to your peers when rated, yet the results are secret seems a bit barmy to me.
However the openess on pay has to be across the board, a few of us volunteering publicly to share will simply be used as a weapon by those who choose not to share.
The anonymous nature of glassdoor tries a different approach. Many corporates benchmark themselves against the wages and benefits of others, but again its cloak and dagger stuff. I mean that information in the hands of a potentially disgruntled workforce leads to all sort of problems for those attempting to keep control of the purse strings. A prime example if the current petrol tanker drivers strike. Fuel companies have to publicly declare their earnings and massive profits, also maybe the bonuses of bosses to shareholders for accountability. Well, thats public information and sure enough those workers down the food chain will say "where is my share?"
However, getting back to glassdoor. There is another side effect that will happen. Clearly people who share what they earn will feel underpaid and be wanting to prove it in general. If the mass amount of data on the site is people who feel underpaid and undervalued then the averages will be low. Those averages will then not help those salaries increase? The opposite may be only the very well paid confess, as an anonymous blag "loadsamoney" style. That make the average insanely high and makes the actually average paid not to badly done by population annoyed along with the undervalued.
Of course the way around this is not individual action, but companies publishing all their salaries, but that is very unlikely to happen.
So we are left with something that really should work, should be done, but seems to be in a place that would take a politician from the West Wing tv programme to sort out.
Yes I have shared mine on there, mainly to feel what it feels like to give that information. Its never really gone well if I have discussed my salary with anyone. People with less experience are bound to think its too much, people with more experience laugh at it and remember back, people with the same or near experience...well they are in competition so who on earth believes anyone.
Lets see where this one goes.