I've created face track data and copied it to the clipboard for Character Animator, as described here: After Effects Help | Face Tracking. However, there seems to be no instruction or clear path as to how to apply that to a character. I don't have a lot of interest in using a webcam to animate, but the promise of lifting data from live footage is worth exploring. Is this just one of the "not fully implemented" features, or am I missing something?
Short answer: Edit > Paste with the target character selected in the timeline.
Full details: see the "To generate face data from prerecorded video" section on page 20 of the Help PDF posted here: Character Animator Help (Preview 1)
You know, it's the first thing I tried, haha. I must have been clicked off of something, because it was consistently grayed out, then I went back, clicked on the character and it was there. I'll echo what others have said about the responsiveness of the program, but I'll chalk that up to it being a preview build (I hope).