From an IM conversation I just had:
(5:38:50 PM) him: quick ?
(5:38:56 PM) me: shoot
(5:39:03 PM) him: does it piss people off when I respond to every fisheye [ed: meant crucible] comment?
(5:39:09 PM) me: not me!
(5:39:24 PM) him: i wish there was a checkbox thingy or something so I can know I've done it
(5:39:31 PM) me: yeah...
So yeah... a checkbox to know your comment has been grokked, and for the reviewee to remember he's grokked it.