The NCSA httpd 0.4 release in 1993 announced support for Group Annotations, which was basically this. So all of you "I had this idea four years ago" people need to get in line behind Marc Andreesen, who had this idea, dear god, 16 years ago.
It never really took off--I think even though httpd supported annotations, I don't think Mosaic itself ever really did.
Of course you can't flap your arms and fly to the moon. After a while you'd run out of air to push against.