From a communications perspective, there is an important distinction to make between online conversations and those of the "over the backyard fence" variety. Online conversations tend to have shelf life. In media terms, that means that it sticks around after the initial conversation takes place, particularly if that conversation occurs in blog comments, on message boards and such.
Sure, the argument can be made that word of mouth can stick with someone over a period of time, but typically WOM is not thought of as a medium with shelf life. Online conversations are thought of that way.
This might seem obvious to many of you, but I wanted to mention it because it's something that clients seem to be latching on to lately. The idea is that along with all the other benefits they would get from participating in conversations online, they would also be building a lasting asset for their product, company and brand.
Sure, message board threads die. So do blog posts. Sometimes they get resurrected, though, especially by people who have similar concerns, questions and whatnot. If indexed, they do show up in search results.
Again, it's something obvious and intuitive from the perspective of folks who have been online or in online marketing for a while. Marketers seem attracted to the concept in part because their investments continue to pay dividends over time and have a cumulative effect that is distinct from that of an online ad campaign.
Something to think about if you're talking to clients about conversational marketing.