the claims on the South China sea are patently ridiculous, but I don't think it can be compared with the senkaku islands. From what I've read China actually did have better claim over those islands prior to 1884 and immediately after WWII, but didn't assert those claims because well.. the islands were worthless. Now that they've found oil they want to roll back the clock.

I think there is a fundamental cultural difference in the way the west and China views the dispute. To the west if you found a piece of land and lived there for 100 years, it's yours - that's how the US was founded after all. But to China it's just the latest in a series of conflicts with Japan going back hundreds of years.