How is Co-Working better than IM/Web/Skype?

I suppose I've missed the boat on co-working. Met several co-working startups at SXSW, met a few also in LA for a conference, and I know it's all the rage in the bay, bay, bay, bay, SF.

What makes co-working so compelling to you?

How is it unlike a self funded Incubator?

What makes it better than working with your partners asynchronously via web/email/im?

Pros/Cons?