Messages 8.0 not showing video icon On brand new Mac running Yosemite, Messages (Version 8.0) not showing video icon at all. No "Video" tab in menu options at the top either.
As Michael points out, if you enable the Bonjour account, the Video Preferences Tab will appear.

Apparently Messages doesn't recognize iCloud accounts as AIM equivalents. No AIM or gChat accounts or their equivalents, no Video Preferences tab and no Buddy Lists.