Word of mouth is great, but in order to get word of mouth you have to have "mouths" that have been to your site in the first place.

You could have the BEST website in the WORLD with the BEST services/products/etc... available at the BEST price and offer TOP NOTCH support...but if you don't advertise in the first place how will anyone go to your site?

Word of mouth is great, but you need to catch the fish before you can share it.