Estates are currently taxed. I believe to the tune of 45% of the amount over $2 million.
As far as capital gains goes, they are due when you sell your capital. In the case of PG this most likely occurred when he sold ViaWeb. Everytime Larry and Sergey sell their GOOG stock they incur captial gains.
Obama is generally proposing raising the capital gains tax from 15% to 20% for anyone that earns over $250,000. Any startup founder that has a successful exit should make a heck of a lot more then $250k. By def an angel investor must earn $200k per year or have a net work of more than $1 million.
And that is why I want to see the details.