This is going to lead to some kind of right-wing freakout:
The key scene takes place in “The Incident,” a short story in Action Comics #900 written by David S. Goyer with art by Miguel Sepulveda. In it, Superman consults with the President’s national security advisor, who is incensed that Superman appeared in Tehran to non-violently support the protesters demonstrating against the Iranian regime, no doubt an analogue for the recent real-life protests in the Middle East. However, since Superman is viewed as an American icon in the DC Universe as well as our own, the Iranian government has construed his actions as the will of the American President, and indeed, an act of war.
This is a cute scenario, particularly given that the Obama administration has been so concerned with supporting Iran's democratic movement without enabling Iran's hardliners. Various comic book writers have explored the idea of Superman as a strategic deterrent to America's enemies, but it's also logical that being associated with American power would diminish his utility as a symbol of justice in places where America isn't very well liked.
Aside from the legal issues with this, the problem is that Superman's solution wouldn't really solve the problem. Superman is already too closely associated with American power for this to matter. Instead this is just likely to arouse more suspicion as people wonder if this is all a calculated move to increase American influence in areas of the world where people regard the U.S. with suspicion.
I haven't read the comic yet, but there's at least one other issue here: Clark Kent can't renounce his citizenship for obvious reasons, because doing so would reveal his secret identity. So at least as Clark Kent, Superman would go on living and working in the United States and presumably paying taxes. Since Superman is a persona, and Smallville farmboy Clark Kent is arguably the more core element of his personality, Superman would be giving up his citizenship in only a symbolic sense.
