With the Title Update 1.02 patch, Rockstar also announced that they were going to release a new multiplayer mode, the Hardcore Free Roam mode. This was something the community had been asking for since day one. In Hardcore Free Roam you can not use Casual or Normal targeting, only Expert is allowed. This means that your aim will never snap to a target, and you'll have to manually guide the aim.
If you're currently on the Xbox 360 or PS3, you'll have to restart the game for the new playlist to show up. Once you've done that, you can play!