Urban chase Skill Challenges + Group skill checks

The section on Skill Challenge group skill checks in the DMG mentions that a group skill check should be used when every PC must perform a given action, such as climbing a wall. I had concluded from this that if the PCs were chasing someone, then whenever someone decided to just use Athletics to run really fast, the other PCs would help this PC (the lead runner), and the group would move together as a whole.

But in his blog post on Skill Challenges from last week (http://gloomforge.livejournal.com/12135.html), Keith Baker explicitly used this example as one where he would make each PC roll individually (in the Aid Another paragraph).

So, how would you run it?
1. PC rolls alone. Success = Moves ahead of the other PCs. PCs get 1 success for the challenge.
2. PC rolls alone. Success = Moves ahead of the other PCs. PCs only get a success when they've all moved ahead.
3. PC rolls alone. Success = All PCs move ahead. PCs get 1 success for the challenge.
4. PC rolls, but other PCs can help. Success = All PCs move ahead. PCs get 1 success for the challenge.

Barring odd bardlike effects, one character can't make another one run faster. (Counter-argument: A grizzly bear CAN, in fact, make a man run faster)

No aid another for that Athletics check in my opinion. Streetwise (I know a shortcut) would help, though. Other skills might include Bluff or Intimidate to cause the quarry to hesitate or look over his shoulder, or a ranged attack roll to throw something at him.

1. or 2., depending on the nature of the prey. If a single character could take him down (a random pickpocket), then 1. If the PARTY needs to catch him, then 2.

It really depends on the circumstances. I wouldn't really consider a flat-out sprint over open terrain a skill challenge. That's more like a single opposed skill check.

However, if the PCs are chasing someone through a crowded city, successful rolls could indicate noticing which way they ran, taking a shortcut, or convincing townsfolk to slow them down for you. In this case, each roll would equal either a success, or count as an Aid Another check.

Another example is a wagon-chase, or a ship-chase where each member of the group could conceivably contribute to the success of the entire group.

I think you're looking at this in stark black and white, unimaginative terms. Think about how a pack of lions chase a gazelle. They don't all run flat out and the first one to get it gets the kill. Likewise the Gazelle doesn't run straight, flat out sprinting until it gets away or is eaten. Lions (and heroes chasing someone through the streets) can use group tactics and coordinate their attacks - a few lions will attack frontally, while others wait in flanking positions. Not more than a third of the lions will ever be running fast at any given time - they spend only enough energy to keep the gazelle moving. The lone gazelle who is running at a sprint will tire far faster than the pack of 5 lions who can take turns keeping up the pursuit.

Have one person chasing the villain (Fighter - Athletics Roll). A second can cut through the ally and cut him off when he runs down the main street (Rogue - Acrobatics Roll to jump over the fence in the ally). The villain turns, and tries to run back the other way, toppling carts and barrels to slow his main pursuer. The wizard, knowing that the market is nearby and is very crowed, yells to his friends to try and chase him down that direction (Streetwise Roll). The cleric hears the advice, and pleads with the crowd to block the villain (Diplomacy Roll), forcing him down a different street into the crowded market. The Fighter stays hot on his heels, and tries to scream at him, telling him what horrible tortures he's going to do to him when he catches him (Intimidate Roll). The villain hears the taunting, and while looking back over his shoulder, he accidentally runs smack into a produce wagon. The rogue sees and opportunity, and cuts back through the ally, swerving to avoid people, and tries to clear a path by shouting "plague" (Bluff Roll). The crowds disperse, allowing the party a clear path through the market as the villain is struggling to fight through them. Eventually, after enough successes, the party can finally nab the villain. The fighter makes one last roll, Athletics, as he is in full sprint, and jumps onto a wagon, then takes a flying leap to tackle the villain.

You need to exercise your imagination when roleplaying these skill challenges. The urban chase is super exciting when played out with imaginative players and Dungeon Master - and if the DM is clever enough in his descriptions, it can be as memorable as any combat.

As per Keith's blog, yes, this is all an example of where Aid Another might not work. The wizard cannot aid another to help his rogue companion run down the ally and jump the fence. The wizard is not approaching this challenge that way, he's using that big brain to determine how to cause the villain to meet with obstacles and allow his companions to catch up - remember, he's the controller, keep your role even in skill challenges. Few wizards solve any problems by leaping fences and tackling people - but that doesn't mean that the wizard cannot assist in the chase.