Several news agencies have been reporting on the possibility of selling 100 F-22 Raptors to Japan. The reaction from Korea is one of skepticism. From the Korean perspective, this would create instability in East Asia by giving Japan air superiority over China and Korea. I also think that, coupled with the gradual reduction of U.S. troops in Korea, it will appear to weaken the U.S.-Korea security alliance. The Korean air force currenty uses F-15's, which are like a million years old (actually, about 35, but that's still old).
But from the U.S. perspective, this sale makes a lot of sense. First, these planes don't come cheap (over $300 million each). The original plan was for the U.S. to purchase over 700 of them, but that number was drasticaly reduced during the Clinton years and I think the plan now is to purchase less than 200. So this sale will make up for much of the loss to the sweet tune of $30 billion. And second, this will strengthen security relations with what is arguably our second most important ally. There are concerns over exporting such high tech weaponry, but I would assume that the models sold to Japan wouldn't contain the most secret technology so they would be getting the "Diet" models of these fighters anyway.
From what I can tell, these fighters are AMAZING. Their main asset is their stealth technology, which means that they can shoot down enemy planes before they're detected. Tests indicate that they will absolutely destroy the current fighters on the market, and you would only need a couple of them to wipe out entire squadrons of enemy fighters.