I've had a few times where pulling aggro quickly was needed. I've done it like Synn says and it works but don't forget about concussive shot as well. First, if your tank has more aggro than you after the concussive shot, the target will be slowed (of course this doesn't work on bosses but bosses don't get CC'd either... ^_^). Second, it lets you pump 2-3 more shots into the target before they reach you or the tank, letting you get more aggro built up. Distracting shot can be one of those to build up the aggro but it triggers the GCD so distracting is among the last I use if I have time and everything else is on CD. With concussive, crits and a well placed trap, I've iced targets at more than 5k threat. Admittedly, it's not something you WANT to do all that often, but there are times it comes in handy.
I've noticed that concussive shot is very under-utilized by most hunters but I love it. I can drop most targets before they even get to me. I enjoy using it as an opening shot. I only use distracting when I'm desperate for a shot that will up my aggro level and my others are on CD. That is not very often.