What virality plan?
At least, that's what I got from fast-forwarding, it's an hour long presentation.
My point is that trying to spread an app aimed at enterprises using a large-scale bottom-up approach seems to be a relatively unexplored approach. I don't know how Yammer is doing, but I have never seen one of my business partners or co-workers use Yammer and thus be exposed to it (=bottom-up).