Garrett Smith, one of the smartest people writing about VoIP out there, had an interesting post a few weeks ago, about the use of video calling:
"Propelled by the "seeing is believing" phenomena, video phone calling is continuing to increase in popularity and usage. It's growing adoption, however, is not being driven by traditional consumer calling (as one would think), but by niche applications."
Garrett also provides several examples of such niche applications - some of which I haven't known about until I read his post. While I don't refute the fact that video calling is used for a wide variety of niche applications, I think the analysis is a bit misleading.
I've discussed it here already, when I was analyzing whether video telephony adoption is a matter of better user experience or more use cases.