Sanford Dickert has an interesting post, titled (but it wanders off!): Millennial Makeover: Is there a Lincoln or FDR in the 2008 race?
(Irrelevant answer: Not unless you believe Hillary is; Obama is GenX. But I'll get to that in a moment, and why that's spectacularly great news as my second point.)
First: Why GenX is the Entrepreneurial Engine
In the post Sanford makes a few points, mostly about the turning over of generational cycles that are coincident with technological breakthroughs.
So again to point this out: the technological breakthroughs you see are directly a result of GenX (and equivalent Reactive generations) opting out or being shut out by the generations that precede them. This forces a huge entrepreneurial upswell each time. Why are they shut out? It's complicated, but the theory has a lot to do with society in general becoming far less cohesive (riotous, actually) when the Reactive cycle (GenX) are children, and so the kids in these generations tend to grow up fending for themselves and without any clear social norms to strive for. It's one thing to leave home as a hippie when you're 15... there's a home to leave, standards that have been drummed into you. It's another to cobble together an ersatz family structure as you go.