The ROK’s ambassador to Japan has returned home in protest:
In response to the Japanese government’s decision to include Takeshima explicitly in a new guidebook for educators at the junior-high level, President Myung-bak Li expressed his “deep despair and regret” on 14 July and instructed the appropriate federal entities to “respond decisively.” On 15 July, Seoul will temporarily recall Ambassador Chul-hyun Kwon to Korea.
Both Japan and South Korea claim sovereignty over Takeshima (Dokto in Korean), though I think only Korea actually has any kind of presence on them. Wikipedia diplomatically uses a French name for them and avoids entering the fray. There may be undersea fossil fuel deposits near the islands, but they don’t seem to explain the vehemence of the Korean reaction when Japan refers to them as part of its own territory. The Japanese ambassador to the ROK will also be temporarily recalled.