It doesn't bother me but those with more stiff sensitivities in regards to etiquette and grace and everything find it loathsome. I'm sure, the first grunter could have caused a hinderence to other players because of the distractability but todays players are accustomed to it. Talking is distracting but grunting isn't.
Golf is the only sport I can think of that expects silence during play and I have to say, as a spectator, it's the equivalent of watching paint dry. It's the cool thing to do, right now, though, for commentators and spectators to complain about the noise. I don't really get it, but, if it helps them fill the time, then, good for them. I guess, from my American perspective, I don't really worry about things like whether or not athletes are making noises. I'm too busy appreciating their spectacular athleticism. And watching someone compete with absolute passion is entertaining as heck.