This is a good question, and something I have been thinking of a lot lately (as you might have guessed from all my "where should I move?" questions). (Sidenote: oh crap, the Bears just lost
.)
I grew up in a Chicago suburb, and my parents still live in the same house they lived in before I was born, so it is easy for me to call the Chicago area home. Iowa City was "home" for 4 years, but since that was for college, it was more of a home-away-from-home and never "home" for real. Now that I'm back in the Chicago area, it's home as it has always been.
I think, though, that home would be wherever I am at the moment. Although my family is here and most of my friends are here, I think that I could build a home for myself anywhere in the country (I'm very independent, anyway). This is actually very appealing to me lately, and I am seriously thinking about moving my home to some new place. I think that this would be very exciting and satisfying -- to go somewhere where I don't know anyone and to build my own "home" and friendships and life. I think that it would be an accomplishment, but I would still know that I would have a home here to return to if I ever wanted, even though I doubt I ever would, because I think that I would feel that it is taking a step back.
Of course, as I sit here, I am still in the safety net of "home" but I think I'm ready to go somewhere else as soon as I can.