There is clearly a small group of players who will type abusive
comments after losing a game, but I don't think they are exclusive to
ICC, they are everywhere in online chess. I adopted a policy about
two years ago of not talking to my opponents, just show up, play the
game, and sign off, and this has saved me lots of headaches. Once in
a rare while I'll discuss something, but usually not.

I think the vast majority of people who type "good game" have the best
of intentions, but I think this is a chess uncultured thing to do, it
isn't a childhood soccer match, and when I drop my Queen by accident,
resign in disgrace a few moves later, a "good game" from the opponent
is just salt in the wound, but they don't seem to realize it, so I
just ignore it anymore.