In November of last year I upgraded my laptop to a new Macbook Pro Retna 15" from the first generation Macbook Pro from 2006.
The new Macbook Pro feels the same in all the good ways which is a testament to Apple's design abilities. One thing that has changed is the shape of the MagSafe connector that connects the power supply to the computer. When I got my new Macbook Pro, the old one got boxed along with its power supply because it wasn't compatible.
Last week I forgot to bring my power supply to work so I thought about running out to get a new one just to have one at the office, but then I discovered this: the MagSafe to MagSafe 2 Converter
This adapter is quite magnified in this picture. The actual adapter is about the size of a penny. This adapter magnetically clips on to the MagSafe old power supply and changes the shape to be compatible with the new Macbook Pros. It's works great and it's perfect for me since I think I had at least two of the old adapters around from the seven years I had my old Macbook Pro. Now, it'll save me the time and trouble of unplugging my power supply from home and bringing it to work.