Running swimmingly here, on the base 13" with 8GB RAM, minus one nagging issue. While my keyboard backlight automatically adjusts, I have yet to see my display do the same thing, even after an SMC reset. Thinking back though, it may have been wonky even under 10.7.4. Other than that, animations are smoother, the machine is quicker to boot, and overall it feels like these Airs were made with ML in mind.