Australian Open has decided to name and shame the worst offenders and Roger Federer is in the bottom 10 of 41 players.
Djokovic achieved a success rate of 60% and Nadal had 73% success rate, both of which are exceptional. Nadal and Djokovic made the Top 10 and are in reality ranked 1 and 2 as the players above them made so few challenges and/or were eliminated early in the tournament that their results are statistically insignificant.
Federer made 21 challenges on his route to the semis and was correct ONLY ON 5 occasions (23.8% success rate). No wonder Federer was against it. He either makes those terrible challenges to break the opponents momentum (which worked against Tipsarevic) or he needs his eyes examined.
Most people on MTF will accuse Novak for lack of sportsmanship (ball bouncing, medicals etc.), hell even Federer did, but he should take a better look at some of his own actions.
here's the link