Marketing NPV has an excellent article - Is There a Reliable Way to Measure Word-of-Mouth Marketing? - about the measurement of Word-of-Mouth marketing.
I'm convinced that WOM is here to stay, and that it requires a re-orientation of marketing philosophy in order to make it work. But that for another time.
Here's the take away for me.
Word-of-Mouth is not a stand alone marketing approach. It enhances a more comprehensive method.
What this probably means is that over time more WOM-centric campaigns will emerge that incorporate traditional marketing methods but retooled to fit into a WOM world.
We are at the birth of a new approach. I don't believe it will die from the imprecision of measurement techniques. Rather, I think it will grow because it fits with the way people are functioning in society.
The real key to its success beyond measure will be how it can be developed as an ethical marketing approach. That is a greater question for me.