IMO the SSD is what puts the MBA over the MBP when deciding between the two. The big benefit is the battery life. The MBA is the first laptop I've ever seen where a programmer can work for what amounts to a full day on a single charge without any qualification.
I agree to a point. All of my regular-use apps (Eclipse, Xcode, Textmate, Chrome, Terminal, Echofon) all start up really quickly. I don't really ever find myself sitting around waiting for things on it.
If you do, the prices are a lot more equivalent (ie, MBP+SSD is not cheap).