Kris Myers on http://www.gadling.com/ has an interesting article on what can happen if you return to your home country after having lived in a host country successfully as an expat for many years:

It's possible that you became fully immersed into that host country and culture.

Now, immersing yourself fully in your host country is what globedwelling is all about.

Many globedwellers never return to their native country, but for those who do there are some potential issues. Returning after many years can be just as dificult as moving out and probably most people prepare less for it.

Sometimes, people experience what is known as Reverse Culture Shock when returning to their original homeland: it's a surprising mixture of bewilderment, loss, isolation and confusion. Your home country may no longer feel like home, and you may not feel like you belong there. Preparing for successful "re-entry" often depends upon applying skills of adaptability, change, and flexibility to ease transition back into one's home culture.

The article contains some good advice on these preparations:
http://www.gadling.com/2010/02/08/dealing-with-reverse-culture-shock/