Haha.. I know when I get my iPhone 4 it's gonna be a constant battle to maintain hi-res imagery XD
Then you'll be a little disappointed. It turns out that just about every app that doesn't use only standard UI elements needs to be updated to support HD. Even though these apps are being updated every day, there are still tons of apps that aren't yet supported.
You may think that you can't notice the difference, but you can. Here are two pictures of my app. The first one is the current version available on the app store. The second one is a picture of it with updated graphics running on an iPhone4. Hopefully Apple will approve the update soon, because I think it looks amazing.
And by the way, my lock screen is still the water drops it comes with.