Adobe announced last night (or yesterday depending on where you are in the world!) the release candidate of the next version of Lightroom, 4.3. A good few websites picked up on the line in the release details that noted that Adobe has added HiDpi, aka retina support. However, if you read it fully they add "for the develop module". Anyway, I gave it a quick try out this morning and you do now have retina support in the develop module but not in the library or any other modules, so it's a bit half baked at the moment. It's better than nothing I suppose if you have a retina macbook pro.
The implementation is not great either. When you move between images it loads low res first then renders the full res version. This takes about 3 seconds, which might not sound like much but it's a pretty long time. It does this even if you have 1:1 Previews generated. On top of that, when you move between images in the develop module, they load sharp (i.e. Full res) instantly for a split second, then they go low res for 3 seconds or so and then they go back full res. It feels really slow and clunky, so again, half baked but better than nothing.
By comparison, Aperture doesn't surfer any of these problems. Images load instantly at full res. Now, you would expect this as it's Apple and they had lots of time, but other retina ready graphics apps are pretty smooth too, such as Pixelmator. Anyway, lets hope the next version has full support and improved responsiveness.