Superman renounced his U.S. citizenship

My previous post was about an American university professor who intends to give up his American citizenship and become a naturalized Japanese.
(Click here to read it.)

Well, I just read online that one of the most iconic fictional characters in American pop-culture has just renounced his U.S. citizenship.

In the Action Comics #900 issue (2011 April), which has a cover price of US$5.99 (about ¥486) by the way, Superman announces his plan to give up his American citizenship.

From Action Comics #900

An American professor is turning Japanese

Columbia University professor of Japanese Studies Donald Keene has been teaching and translating the Japanese language since 1955.

He just retired at the age of 88.

Professor Keene's recent press conference with the Japanese media.

Professor Keene made the news in Japan a couple of days ago when he announced that now that he’s retired, he plans to immigrate to Japan and become a naturalized Japanese citizen.

Some of his friends and co-workers in America expressed concerned that now may not be the best time to move to Japan because of the current nuclear power plant disaster. But Dr. Keene replied that, in his opinion, now is the perfect time to show his support for his intended adopted homeland during this hardship.

What do you think about naturalization? Do you think if someone immigrates to another country, they should become a naturalized citizen? Or is a Permanent Resident Visa enough?
If you immigrated somewhere which would you choose?