I saw a good definition of success when researching LETS. Int holds for bitcoin as well.
Money is hard to earn and easy to spend.
Bitcoins are easy to earn but hard to spend.
You can judge the success of bitcoin by how easy it is to spend your bitcoins on something that improves your life.
What's the point of owning 100,000 BTC if you can't buy the occasional, wine, woman or song?
You will have a hard time spending your gold bullion. I wouldn't make the mistake of then assuming you don't want any gold bullion.
This is an important point that people are missing. The success of bitcoin will depend heavily on how easily you can convert between bitcoins and the US dollar. The number of retailers that accept bitcoins is not nearly as important. We need 3 or 4 competing exchanges. Once you have that, market forces will do the rest.