Please no flames... if you don't like it just find something else to do. Didn't see this on here so I thought I would post it. Searched first, but if repost I'll remove.
Probably old as WoW itself, but in all my For The Horde groups I've never seen anyone group here. Considering there is only one way to get up there it's not all that hard to protect the group. Also starting inside the SW gate by jumping off into the lake is a nice way to surprise the Alliance. Done on 3.2.2 with a DK, War Bear Mount, Increased Mount Speed. Can be done without increased mount speed as well, just time the jump better.
EDIT* This is also a nice way around the initial "Stormwind City is Under Attack" message from the opening guards. By the time the guards spot you, you can almost be to the Auction House.
[ame="http://www.youtube.com/watch?v=oOHdLzsRrB4"]YouTube - WoW Hidden "For The Horde" Prep/Regroup Spot 3.2.2 Outside SW[/ame]
From outside SW go to the right until you hit the grass hill. Now aim so you are going towards the top right corner of the SW wall and run. When you hit the top of the hill jump over the gap, you should hit the wall and fall back down slightly. Now run towards the wall/angled towards the top corner and jump ALOT. You will notice you will start to get stuck inside the wall and jump up. Now keep doing this (while still mounted) and eventually you come up ontop of the SW wall. Watch video for better instructions.