In that case, we're hitting it out of the park - over 4 invites sent per user, but these invites convert at ~25%. There's also "k factor" (invites sent x conversion rate), and the interval between user #1 bringing on user #2 is also important... guess there are many ways to present virality :)
That kind of info (4 invites on average per user, 25% conversion rate) is THE critical information. If you want to talk about virality at all, the fact it's not in your presentation is a serious defect you should correct.
