Since this is closely related to the Referral Marketing Boot Camp on Saturday, its important to note a new study from Osterman Research and reports the responses of over 100 online marketers on the state of word of mouth marketing in the US.

appears that there is significant interest in this type of viral
marketing. Fully one-half of US marketers surveyed are using
word-of-mouth marketing at the present time, while 21% are planning to
use it and 14% might use it.

They also see it as important. Almost two-thirds of respondents rate word-of mouth marketing as "extremely" or "very" important.

It seems that their confidence is merited, at least on the consumer side. According to a BIGresearch study from December 2005, word of mouth marketing is the most influential media when it comes to making purchases.

Those marketers who have resisted a word-of-mouth campaign are
mostly likely to cite lack of metrics as a reason, though quite a few
also have difficulty figuring out how to integrate it into their
marketing plan, or don’t have the staff to do word-of-mouth

Clearly, those who use word of mouth marketing expect results
quick. Over 44% say they anticipate the benefits to come in anywhere
from a few weeks to a few days, while a bit under 20% feel it will take
6 months or longer.

More here.