Salary Expectations

Salary expectations are U-shaped along time among quite a few of my friends. Many of us started off after our studies thinking we'd work in rather high-paying consultancies or banks. We realized we want to do something different, and took some salary cuts into account. And ten years on, want to earn what we think is a fair salary. But what is fair? It's such a random issue, and there are so many factors that come into play. What do our partners earn? What do we want to earn? And right now, an issue I may face: what can I even ask for? What am I "worth"?