Retinizer allows apps that aren't Retina-ready and are displayed pixelated at 1x to display their UI widgets at 2x. That way, only their custom images will look bad and not the whole app. To use it, just drag an app (and make sure it's closed) into the window and click the Retinize! button.
It also allows de-retinization of an app, in case it has problems in 2x mode. Just drag an app that you Retinized before and click the button below, which will now read De-retinize.
The app works per-user. That means, retinizing an app in your account will not affect the app in other accounts, where it will display at its usual 1x.
So far, it seems only apps that use Carbon, directly (like Snes9x) or indirectly (wxWidgets, Qt apps) draw their widgets at 1x on a Retina display, while Cocoa apps seem to always draw widgets at 2x. But some apps, such as Eclipse, draw at 1x and use Cocoa (albeit with some weird Java bindings or something like that, not sure). This app also helps in that case.
Please note that this app won't make apps get retina images. That means, custom icons, such as those in the Preferences window, will still look ugly.
It has only been tested with OS X 10.8 but should work fine with 10.7.4.
Updated on Aug 15 2013