Do you want your iPhone apps sharpened up for iPhone 4's Retina Display? iPhone 4 has a whopping 960x480 screen which is literally 4 times (twice vertical, twice horizontal) the pixel size, but the same physical size, as previous generation iPhone 2G, iPhone 3G, and iPhone 3GS. That's a density of over 300dpi -- print magazine quality. Existing apps will just seamlessly use 4 pixels on the iPhone 4 compared to 1 pixel on previous gen iPhones, so they'll look identical.
In fact, fonts -- and if you built your app in Xcode, UI elements -- will automagically be rendered at the new 4x sharpness, so they'll look better.
To truly take advantage of the new display, however, developers and designers will have to go back to the drawing board (or paint program) and make new, higher definition graphical elements like icons, textures, and other artwork.
For some developers this won't even be a question -- they love their apps and they want to make them look as good as possible. They're already getting this done. For others, especially for those with older, catalog apps somewhere in the longer tail of the App Store sales cycle, they may not be sure the effort is financially justified (especially given the 100,000,000 existing, lower res, iOS install base).
So we're curious what our readers, developer and user alike, think? Do you want to see nothing but ultra-sharp apps on your iPhone 4? Do devs need to do it immediately? Wait for the next update? Focus on new apps only? Go back and retrofit old apps? How important is it to you?