I spent my entire childhood moving from state to state in the US, so I've always had an uncertain relationship with "home" anyway. I first came to the UK when I was 14, and liked it well enough, but didn't really think of the possibility of living here.
I came back in 2002 for a visit, and remember thinking how much "foreignness" there was in all the little details of life (oddly-shaped plugs, houses with old temperamental cookers, dryers not being standard in homes, etc.) and thought it was just as well that I lived in the US, since I wouldn't ever really get used to these little details of life in the UK. A year later I was starting a master's course at Oxford, and three years after that I was marrying a Brit and buying a house here. Go figure. Now, another two years have passed and we are probably about to up sticks and move to Switzerland, which is another nice place that doesn't much feel like home.
I don't have a strong desire to move back to the US now, although my husband certainly does, and I would agree to it if the right opportunity presented itself. Even so, there are days when I feel like nowhere else will really seem like "home".