I wrote the following response to another thread (
http://forum.bitcoin.org/index.php?topic=26103.0) that I think has relevance here:
The average customer needs to have a compelling reason to use bitcoin for purchases. Here are few reasons that "could" motivate him:
1. He values the privacy of a bitcoin transaction
2. He prefers to hold his money in his own personal "bank" (wallet) instead of at a traditional (fractional reserve) bank
3. There is a major loss of confidence in his nation's currency
4. He feels that bitcoin is a better store of value than his national currency
5. The vendor offers a discount for customers who pay with bitcoin - (key strategy for vendors who prefer bitcoin!)
6. He likes the "ease of storage" feature of bitcoin
7. He likes the portability feature of bitcoin (especially across national borders)
8. He has philosophical reasons (prefers free-market money over central-planner money)
As noted in the previous post, there doesn't need to be 100% acceptance of bitcoin for everyday exchanges in order for it to be useful. Consider that gold is primarily valued as a "store of value" but that it is not used in everyday exchanges/purchases in any meaningful way. The question then becomes, are bitcoin's features valued enough that people will trade national currencies (and other assets) for them? I think this question has already been answered in the affirmative by the market.
The next major question, in my opinion, is how will attacks from nation states effect bitcoin's value? If it is forced into the black market will it's price go up, as is in the case of illegal drugs, or will its value drop due to fear of prosecution?