Which Mountain Lion OS X feature are you looking forward to most?

Without a doubt, Airplay for the Mac. I've been wanting this for a LONG time. I really enjoy being able to Airplay redirect video from my iPad to my HD TV via Apple TV but up to now you could do that only with iTunes content on your Mac. I subscribe to Hulu Plus to be able to watch my favorite TV programs on MY schedule. Unfortunately, a number of those won't view in the Hulu Plus APP which directs you to view them in the browser on your PC. So I have a Mac Mini wired into the TV VGA input for that. Now that I will be able to airplay, I can re-task that Mac Mini and replace it with a simple Apple TV. I can "dump" the VGA wiring and all will be HDMI.

My wife watches her programs on her Mac and many times the girls have come downstairs to use the "big screen" for a chick flick. We then have to load up what they have selected on their Mac to my Video Center Mac Mini and that's a pain. Now they can just come down with their MacBook Pro's, select Airplay and direct it to the big screen Apple TV. It will be much easier for them to manage without calling on "tech support" (me.)

I'm looking forward to true iCloud integration with the file system. While Dropbox is nice for taking care of the syncing while working on documents on remote machines, something even more tightly integrated with the OS holds some interesting possibilities, particularly for automation (iftt.com hints at some beginnings of this). For example, how about an automatic summary of every article I star in google reader? How about asking Siri to create a report on a particular subject with list of likely links and have it inserted it in Evernote? I wouldn't mind a single command to post my current Keynote presentation to Slideshare as well as a web-based backup set with a sensible URL. In other words, it would be good to have a file system and OS that is less about manipulating and more about delegating.