I can't see any visible changes. It looks like it was an under the hood update. At this point Apple appears to be working out kinks and getting ready for a final release. The Mountain Lion dev previews are about on par in terms of schedule with the Lion dev previews. I think we could see a GM/final release in late June. As for claims of Retina Display Macs, I believe it. I've tried HiDPI mode and the framework seems almost completely in place. There's no doubt at this point.