I think merchants play a bigger role then consumers.
Why?
Well simply if consumers find a lot of merchants accepting bitcon it will create awareness and people will be intrigued.
Visiting the bitcoin.org website they will find so many advantages that they eventually will try it.
I agree with this. More merchants who accepts Bitcoin as a payment option, more people will be curious and will test use of Bitcoin. Much better if there will be a popular online store who will come up with a Bitcoin only day payments to increase awareness of Bitcoins.
Yes, if the online market giants direct start accepting bitcoins means, there are more chances for bitcoin to get spread out to reach non technical people also. It would make bitcoin to become main stream adoption. The price raise of bitcoin will make many merchants to accept bitcoin as a payment.