I was annoyed when I got my MacBook Pro at work and the magsafe magnetic power cord connector was different than the one used on my home MacBook pro. I had to carry my powercord home to use my work computer at home. What a pain! Then our IT guy was like “duh, you can still use the old cord on it, it just looks different.” Well, whattaya know!
On this diagram, my home computer looks like C, and my work one looks like A, but they are interchangeable.
Image via TUAW
I guess I like the updated connector better. With the older one the cord sticks straight out and then has to bend, which can be an issue. With the newer one, the connector is slimmed down more and the cord sticks straight back without having to bend.