I'm using two addons. The 'arrow' is done by a Ace2 mod called Cartographer, the paticular module for is called Waypoints.

I use another mod called Lightheaded, which has the Wowhead comments for every quest in it, so I click on a quest in my quest log, read thru the wow head comments (all in game) and if someone has posted a loc to an objective, I click the loc and it sets me a waypoint and shows me the way to go.

Pretty bullshit, by awesome mod.