Considering there is probably a vintage effect, and currently 5% of YC companies are worth over $100 million, that means that most likely 5-10% of founders that join YC will become millionaires over time. That's pretty impressive.
Though, I do wonder, how feasible would it be to end up with a 2+mill nest egg(or however much you need to live off the gains) by ~35 and retire right then and there.
Edit: Forgot a word.