At 3% equity, he would need either a really, really big hit or a lot of big successes to become a billionaire. From YC's modus operandum, I think pg cares more about shaking up Silicon Valley than he does about maximising return on investment.

maybe if YC were acquired by another VC firm, he might be able to get a large multiple off of his ownership stake.

either way, that would be cool to see pg become a billionaire. I wonder how he would shake up philanthropy? He might be able to find a better charity model than what currently exists today..

The most efficient way to help homeless people is to walk up to them on the street and give them money. Not much room there for innovation. On the other hand, the cheapest way for society to help "permanently" homeless people is to pay their rent on an apartment. That might be more interesting.

Give them anything but money.

It's a small pilot project but it went really well: http://www.economist.com/node/17420321?story_id=17420321

And, with the standard Malcolm Gladwell disclaimer, http://www.gladwell.com/2006/2006_02_13_a_murray.html seems to indicate than most homeless people aren't homeless for very long.