I plan on doing the same thing...but at the side of my garage.
Last Fall I poured the driveway but the area to the side of the garage was left until I decide exactly how I want to complete it.
I plan on pouring concrete but leaving a gravel area similar to whatgroucho did so I can park my Jeep (if it leaks) and also have an area where I can do some dirty work...painting small parts, washing greasy oil stuff and the likes.