I don't play online so it's not an issue for me, but I'd be pretty mad.
(On the other hand, cheating offline is really fun and something I encourage :</>D)
Why? It sucks the fun right out of the game! ;-;
That depends on a whole heck of a lot of factors. I can tell you right now though, being massively overpowered, or cheating outright, can be epic fun in some games.