Opportunity is knocking. Should I open the door?

infinite9 writes: "I hear about startups all the time. But most of the time, it's just talk. So I don't take them seriously. But this time, someone has really caught my attention. I'm an independant IT consultant with many years of experience. I'm in my 30s. I make an excellent hourly rate and would most likely continue to do so. But a friend of mine has offered me part ownership as a founding share holder in a new business. I can't talk about what I would be doing, but it's spectacularly awesome. It's the stuff I dreamed about making when I was a kid. I'm usually very skeptical about these things. But in this case, their business plan is rock solid. They have several investors interested already. But when I heard about one potential investor in particular who they've already met with, it floored me. Everyone here would instantly recognize his name. If this person trusts these people and their business plan, shouldn't I? Here's the problem. For the first few years, I would be making what for most people is a great salary. But for me, it's a significant pay cut, almost half. But I'd be working from home a lot. I'd have a lot of control. I'd be working with my friends doing something extremely fun and satisfying. Currently, I put quite a lot of money a year in an IRA/401k. I'd have to stop that. But in exchange I'd get quite a lot of shares. If they just hit the conservative estimates in their business plan, i'd be very comfortable. If they exceed plan even a little, which is likely if they succeed, I'd never have to work again. Worst case, I walk away with valuable business experience, good technical experience, and no IRA/401k. I would be around 40 at this point. So what would you need to justify leaving your comfort zone and taking a risk like this? Other than obvious due diligence, what would you want to know or consider up front?"