This was certainly unexpected. I had to read the headline twice to make sure it wasn't an early April Fool's joke.
Apple is pumping the Mac OS full of iOS steroids and cementing social media integration. Some of my Mac using friends have now decided to skip OS 10.7 Lion in favor of OS 10.8 ML. The winter release being one of the deciding factors.
Tried Messages Beta and it works. I'm also assuming that Core 2 Duo CPUs will be the minimum hardware requirement to run ML.