The personal value factor in viral apps

David Beisel talks about what makes an online service viral and proposes 3 variables that determine the viral adoption of an online service:

Viral adoption = (how inherently sharable x how easily sharable) x (integration of sharing into content/service)

Agreed on all 3, but I think David is missing the #1 factor that determines the success of the viral adoption: the personal value factor.  Both LinkedIn and IM would score similarly on David's formula above (both are inherently sharable, both are easy to share and in both examples the sharing is extremely integrated into the service). However, the personal value derived by having my friends on the same IM service as I use is 100x greater than the personal value I gain by having each and every one of my friends on LinkedIn (and btw - I'm a big LinkedIn fan). That's the primary reason for ICQ, AIM, etc having quite a few more active users than LinkedIn...

Or as Joshua Porter noted a while back:

From now on I’m going to call this idea the “Del.icio.us Lesson”. This is the lesson that personal value precedes network value: that selfish use comes before shared use. We’re seeing it more and more everyday in services like Del.icio.us, Flickr, and is an interesting aspect of networked applications. Even though we’re definitely benefitting from the value of networked software, we’re still not doing so unless the software is valuable to us on a personal level first.