I do not know if many comments are actually flagged and deleted.
But if many are deleted due to flagging, then what about showing
those using some strikethrough and an explanatory tooltip for
(say) one more hour? That way, everyone can learn from it:
Mockup of deleted comment  Some thoughts on that:  For example
"+1" and "belongs on" comments may be flagged for automatic
removal without the commenter being notified, nor punished. For
the "+1" comments Jeff wrote in August 2009:  I'm actually ok
with flagging meaningless comments like this, since    • there's
no actual penalty to the user when a flagged comment is removed
• the flagging comment process is basically 100% automated and
doesn't require any mod intervention  [..] added "noise" as
reason for comment flagging. Please use it on egregious non-
value add comments that are noise and not signal.  I assume this
works fine, but neither the original commenter nor the rest of
the audience might notice that things have been deleted. Also,
temporarily showin