Zimmerman's a ball player. It's no surprise he's looked good at 1st base. He's one of those players that can play anywhere. If it involves a baseball and a glove he can catch it, hit it, throw it... well he doesn't have to throw it anymore. Just catch it and hit it. And he can do that no matter where you put him.
I thought he was great in the outfield last year. He's especially good at diving catches and stops. As he's shown at 3rd, OF, and already at first.