The new LFG window now requires you to select options for your group role: damage, tank, and healer.
In this shot, taken by a Warlock, only the "damage" option can be selected, the rest are grayed out.
Another look at the LFG menu. In this shot, the Paladin can choose any of the options: damage, tank, or healer. Note that you can choose multiple options if your class is capable of filling multiple roles.
The new "Leader" checkbox indicates whether or not you're interested in being a group leader.