In Diablo II, you had to "touch"/click the waypoint as if you were using it to "find" it, adding it to your waypoint list. I know that Diablo III waypoints reset based on the quest, but are waypoints acknowledged automatically upon passing them, or must they be "touched"? If they don't have to be touched, what distance still qualifies as having found the waypoint, and can party members get waypoints for the whole team? Would the whole party get the waypoints even if they weren't there at the waypoint itself, or say, in town while the rest of the party was working through the zone?
There is no need to actually click on the waypoint -- simply moving close to it is enough to activate it. This is a large visual and audio effect with pulses of blue light and sound, so it's very easy to tell when you have successfully activated a waypoint.
In multiplayer, you can teleport to any other player, so even if activating waypoints doesn't unlock them for all active players, all you need to do is teleport to your friend to immediately unlock the waypoint yourself.