An early employee will get about a percent tops as an individual contributor...maybe up to five percent tops if he is more of a vp engineering. In exchange, a seriously below market salary, equally high if not higher risk of losing one's job vs. founders, and vastly less respect when he later goes to try to do his own startup.
Assuming the same caliber of individual, it makes a lot more sense to either found your own startup, or join after real financing (where you get a market salary, and have a lot less risk, plus a lot of startups with problems have been shaken out.).
Obviously being am early employee at a great startup like google or Facebook makes sense, but for companies more likely going for 10 to 50m base hits, I don't think early employee is a financially rational decision. (note to future people I want to hire: I only do high risk potentially high value exit startups, so your initial equity actually is worth it!)