I use a 15in Macbook Retina as my "desktop" computer, lugging it most days to and from work. However, when possible I try to get by with just my iPad 3 + Logitech Ultrathin keyboard. Days when I'm traveling in and out on the same day, or when I have a lot of offsite meetings, I try hard to only bring the iPad.
I'm still trying to figure out how an iPad mini-sized tablet might fit in, but as of today I can't see it. Of course, there was a time when I didn't think I'd use a tablet much at all, and here I am creating this branch on one. So...we'll see.