Say Amazon take bitcoin tomorrow, it would still be an extra step and an extra conversion charge for the general public to use bitcoins. Unless they got paid in bitcoin and they would be pretty sick now if their salary was set at the value of 1200$/b.
Buying things from overseas? it simplifies I guess. But you lose any protection.
Sending money to someone far away. Not an everyday thing for general p.
Imagine if you have fairly grown up kids, but not grown up enough that you want to let them loose on the net with a credit card, but old enough that the amount of internet purchases they make far exceeds what you want to have to deal with. Bitcoin.
Imagine if you're a respectable mum or dad in a conservative neighborhood, but you just happen to love spending Sundays in your basement busting your whatever to german scheisse movies. Bitcoin.
Imagine that you found this marvelous doohickey that costs next to nothing on a site you don't trust. Bitcoin.
Imagine if you have a cousin somewhere in Africa or Asia who needs to get out of the country ASAP because shit's going down, or simply suddenly ran into some economic dire straits. Bitcoin.
Imagine.... use your imagination!
For crying out loud...
Now imagine that worldwide.
And after all that explain why it's market cap should be less than say western union alone?
I think the problem in valuation is the initial distribution (aka the inflation of 3600 new mined BTC daily). That's a lot of coins looking for a holder even on a slow day. So BTC will be a wild ride, but it's a necessary evil and only temporary can't wait for (76 weeks, 5 days, 22 hours, 20 minutes) http://bitcoinclock.com expecting it to have a huge effect on valuation once we'll start getting closer to that
Hopefully liquidity is such, by that time, that we won't even notce.