Building those foundational relationships requires conversation. 

Well, the statement may not have shattered your preconceptions about Word of Mouth Marketing, but the emphasis on conversation does help explain why Word of Mouth is currently more prominent in offline, face-to-face relationships.  Conversing through online video and chat rooms is not necessarily less personal than real world engagement, but it does lack the important integer of spontaneity...That same spontaneity that allows you to connect with an old friend at the electronics store and evangelize the 54" LCD you purchased last year. 

A number of web solutions have attempted to provide an environment conducive to spontaneous meetings.  Me.dium allows users to follow friends to different online destinations.  Heavily populated virtual environments create an opportunity to naturally encounter acquaintances.  For the average user, however, downloading Second Life or allowing friends to follow your browsing history is not enticing or likely in the near future. 

An alternative to the full immersion of Me.dium and virtual environments is a forthcoming feature from messaging startup Meebo called Community IM.  As Venture Beat's Eric Eldon reports, Community IM is a "white-label platform where other sites can offer their own web-based IM services."  In other words, sites can chose to integrate Meebo's new feature enabling users to chat with friends with transferring to an external client.  Initial partners are MyYearbook, Piczo, and Flixster which may allow for some spontaneous connections.  The true value for Digital Word of Mouth, however, will occur when messaging communities are integrated into retail sites.  Then you can finally encounter a friend shopping for electronics and remark on the great performance of your own 54" LCD.  

Disclaimer: The author does not own a 54" LCD but does enjoy using the inch notation multiple times during a post.