If an app isn't optimized for Retina-display Macs, at worse it will appear as pixel-doubled. Pixel-doubling on the whole app (including UI elements like text) will only happen on older games written for older APIs.
That said, I have not had time to look over the GPU plug-ins on PCSX-R to see how well they perform in Retina, mostly because I don't have a Mac with a Retina display.
That said, I have not had time to look over the GPU plug-ins on PCSX-R to see how well they perform in Retina, mostly because I don't have a Mac with a Retina display.