John Gruber in his iPad mini review:
Both the 11-inch Air and full-size iPad 3/4 make more sense to me as devices for people who only want to carry one portable computer. But if I’m going to carry both, I think it makes more sense to get a bigger MacBook and the smaller iPad Mini.
I’ve been thinking about this quite a bit the past week. I have been carrying around an iPad (3) and 13-inch MacBook Air for most of the past year. (The Retina 15-inch MacBook Pro is my desktop machine for now.) But I think I’m going to change things up. I think I’m going to go with a 13-inch Retina MacBook Pro (review forthcoming) and the iPad mini in my bag. Power + Portability.
For trips, I think I’ll still just take the regular-size iPad, when all I basically want to do is check the web, do some email, and write. Still thinking all this through though.