Preview doesn't seem to be very retina-aware. On my retina iMac if I take a photo it by default will open it smaller than true resolution, i.e. not pixel-for-pixel. If I choose "actual size" it ISN'T actual size, it's blown up bigger. This is with my riMac at "best for display" settings. Most all my other photo-savvy applications, Photoshop, Graphic Converter, LilyView, Lightroom, Aperture, etc, will be smart enough to continue to show UI elements properly but show the photo pixel-for-pixel. What's the problem with Preview? I can understand a browser like Safari not getting it, but Preview can be set as the default viewer for many images.