A look at some of the resources from Apple’s new Messages app shows several graphics that come in multi-part TIFFs that include regular and double resolution versions. In fact, if you look at the information embedded within the images, you can see the resources were at one point named in the same “@2x” convention. So, it seems Apple’s Messages App is already building in support for Retina displays on the Mac.
Dustin Curtis found a few @2x Retina images in Messages. If there is a Retina Mac in the works I think the first to come out will be the 13.3-inch 2880×1800 MacBook Pro. But I’m not sure if the existence of Retina assets in OS X is a definitive indication that Apple is working on Macs with Retina displays. For instance Retina display-equipped iOS devices remotely accessing OS X will need Retina assets to render at the appropriate size.