The service itself is not about virality, but their customers are people who want their video to become viral, and for a video to become viral it needs exposure to key figures, which you might reach using their 'AdSense' network.

Here key figures means people who are interested in your video, have the personality to share videos and are charming enough to have a following that enjoys them (and perhaps includes more key figures).

Also there Virool guys seem to have spend a rather large fraction of their seed finance on the video funny that sells their service :P