Head on over to Apple and watch the video walkthrough. Here are some of my immediate thoughts:

AirPlay Mirroring

AirPlay Mirroring is probably the one thing that excite me the most. It’s exactly what I’ve been waiting for. At work, we have this big mess when we are connecting computers to TV’s, with different wires and inputs and other connection problems. Now we can throw all that way and just buy an Apple TV for each TV.

Messages

A very welcome addition. I was disappointed when iChat didn’t get a big upgrade for the Lion-release, so I’m glad they are killing it and launching this instead. Download the beta.

Gatekeeper

Gatekeeper is a new security feature, which among it’s many different settings, let’s the user choose the following:

• Only install apps from the Mac App Store
• Only install apps from the Mac App Store and identified developers (developers has to digitally sign their apps)
• Install apps from anywhere

I’m very interested to see which of the three possibilities will be default one when you buy a new Mac. Gatekeeper also hints to a possible future, one with the last option removed. I don’t think that will happen though. It’s too drastic for OS X as a platform, which will be much smaller than iOS going into the future. OS X is only going to be used in work-type situations, where people need powerful and bigger tools than they can get on a tablet-type computer. But that’s a discussion for a different time and place.

Update: John Gruber reports that the second one is the default.

Notifications

Yep, this one made perfect sense. Feel sorry for the guys behind Growl though.

All in all, seems like OS X Mountain Lion is going to be a great release.