Man. Sharing details of all online activity by default is CREEPY bengoldacre.posterous.com/spotify-seems-… RT
— ben goldacre (@bengoldacre) August 4, 2012
This morning I read Tom Morris' post on a new (to me) feature in Quora which shares with other users which questions you've been reading. Being a social tool there's an argument to be made that Quora's behaving quite normally in doing this. Some people have apparently been in uproar about this and have quit Quora - which as Tom points out is a bit of an overreaction given that you can just switch off this setting. I checked to see what setting I had on mine and found it was already off (presumably by default as I'd not known anything about it until I saw Tom's post).
Edit: 14 August - I've just spotted an option in LinkedIn which jobhunters might want to be aware of, "Activity broadcasts":
By selecting this option, your activity updates will be shared in your activity feed.
Let people know when you change your profile, make recommendations, or follow companies
Note: You may want to turn this option off if you're looking for a job and don't want your present employer to see that you're updating your profile.