I'm sure that I am not an only reader not familiar with YouTube's Who's Watching Now feature.

It's shows who is watching video "Never before seen Video of WTC 9/11 attack" with me ;-) (not a registered YouTube user).

It was expected that ActiveSharing is not enabled by default:
http://www.youtube.com/activesharing_about

Is the average user using this feature?

I've found ActiveSharing to not really be a feature because YouTube doesn't really have any collaborative features on the video page.

I had enabled it but disabled it earlier today as it was just irritating telling me that I was watching a video (duh!).

Thanks for sharing.

Yes, it doesn't sound good. We can't know what kind of people are "tracking" what videos users are watching, Someone can take a screenshot, put it to his or hers blog and show what this YouTube user is watching. Not good!

I stopped using it because once I was sent to a lesbian video, and I didn't liked that to be shown when someone looks at my profile... In google history you can erase particular items you don't want to be shown (but anyway, it's not public); but here the only thing you can do is erase the whole log, and I don't like that.
So now is disabled for me.