"Under the hood"? Not really. There are a few nifty new APIs – SceneKit, NSXPCConnection, NSUserNotification, the sharing stuff – and the 64-bit kernel (with kernel ASLR) is now the default. Regarding user-visible features, I think there are a couple nice ones:

- AirPlay mirroring is slick, especially in meeting situations

- Document auto-save and versioning are a lot less annoying and more useful

- Improved sharing support can be quite useful in many situations

- Calendar and Contacts suck less

- Gatekeeper is, I honestly believe, a solid step forward in improving system integrity and security

- iCloud sucks less and is better integrated into some system apps

- You are now notified of both system and app updates, and update checks happen daily. I think this is huge for app developers

- Preview has support for entering text in text fields of PDF documents which aren't true PDF forms (this honestly might be my single favorite Mountain Lion feature)

For $20, I think this is a solid "polish" upgrade. There's nothing mind blowing, but there's an incredible amount of polish across the system, with a few truly useful features mixed in. For me? Money well spent.

AirPlay mirroring sounds nice. Could it be used to show Photoshop canvas on an iPad when drawing with wacom?

I was thinking of buying an app for this, but if Mountain Lion does that I might hold off till I upgrade.

Out of the box (so to speak), AirPlay mirroring only supports traditional AirPlay destinations, e.g. AppleTVs. I'm pretty sure you'll still want to pick up that app which makes an iPad an AirPlay destination.

Also keep in mind that AirPlay mirroring requires at least a Sandybridge CPU, so you need a mac released in 2011 or later.

Can you cite a source for that? Experience suggests that is not the case.

http://www.apple.com/osx/specs/ lists the following macs as supporing AirPlay

  * iMac (Mid 2011 or newer)
  * Mac mini (Mid 2011 or newer)
  * MacBook Air (Mid 2011 or newer)
  * MacBook Pro (Early 2011 or newer)

I remember reading that AirPlay mirroring uses the video encoding capabilities of SandyBridge CPUs, but I can't find a source for that now. Anecdotally, http://airparrot.com really taxes my 2010 MacBook's CPU.

Strange, because it's working great on my 2008 unibody Macbook Pro with Core 2 Duo.

Searching "airplay mirroring mountain sandy bridge" suggests otherwise.

http://www.google.com/search?q=airplay+mirroring+mountain+sa...

http://www.mindofthegeek.com/2012/07/05/airplay-mirroring-in...

Integrated iMessage is all the extra features I need.

Safari uses Core Animation for rendering, much smoother scrolling. It also has a sort of "Tab expose" feature.

and shared tabs through iCloud to your iOS devices.

Been using it on a fully loaded macbook air. Completely anecdotal but I think my boot times are faster. But my encryption seems slower. Safari is wayyy more stable and faster. Messages is integrated better and love Notifications!

Launchpad is way smoother imho.

Does Messages work through a proxy yet? That was driving me nuts when I was playing with it in beta.

Is Mission Control any faster in switching spaces? It's incredibly annoying to wait 2-3 seconds to switch spaces, every, time. Especially since it was configurable in Snow Leopard.

This really bothers me too on an air where I'm switching back and forth from fullscreened terminal to browser constantly. Fine, it looks an feels quite cool when combined with a swipe, but it's really sluggish when you switch with assigned keys instead..

On Lion machines, using the keyboard shortcuts (ctrl/cmd+1/2/3/4), switching spaces is well under a second (my guess would be 500~750ms). From MC (which takes again less than a second to enter), entering a space is more in the 750~1000ms range but still, I don't know where you get that 2~3s figure.

This may help, although I found too fast an animation makes me dizzy after a while.

    defaults write com.apple.dock expose-animation-duration -float 0.15; killall Dock

That's the mission control expose animation, I know of that and use it. I want the four finger swipe sped up. I don't know the absolute numbering of my spaces, it's a relative association for me.

> I want the four finger swipe sped up.

Ok, I never use that one. Sadly it seems that for the sake of consistency with the physical world this animation is tied to the movement of your hand (whereas the MC exposé swipe is a trigger).

> I don't know the absolute numbering of my spaces, it's a relative association for me.

One can set up "Move Left/Right a Space" shortcuts in the Keyboard prefpane. Same animation speed as the swipe, which feels ungodly slow.

I haven't tried the GM but on DP4 it felt like the animation takes even longer than on Lion. It moves at the same speed but the 'settling' time when it's slowing down is much, much longer. I'm talking half-a-second-longer longer.

Being unable to cycle through windows with tab in exposé is what really hacks me off about Lion at the moment.

They've hardened OS X's security model a lot. Gatekeeper + new IPC system (XPC) is great. But the best thing is App Sandbox. They've introduced a lot of new entitlements, like "file bookmarks" that'll make it easy and virtually pain free for most apps to embrace Sandbox. Also, Sandboxed apps can now be "Scriptable" - so users can put scripts in a folder in ~/Library/User App Scripts/com.apple.qt and those scripts will execute "without" any restrictions (i.e. outside of Sandbox). The rationale is that users have intentionally put those scripts in that folder (apps don't have access to that folder), so it's OK to run them.

Application Groups: you (or OmniGroup) can mark multiple apps with the same developer ID, and they can share files, use IPC/XPC directly, a shared file system location for user data, etc.

You can watch session 700 at WWDC 2012[1] that's I (poorly) summarized above.

I think OpenGL on OS X is also upgraded to 4.0 on ML, but I'm not sure. Siracusa's review at Ars (when published later today) will tell us if it's true or not.

[1]: http://developer.apple.com/videos/wwdc/2012/

Yeah, a list of bug fixes would be great. I'm still having issues with reconnecting (after sleep, on startup, ...) to wifi on my air. Also the problem with fans (who apparently think they are propellers on a WW2 bomber) remains to be solved. If this update fixes this I'll upgrade just for that (since apparently Apple can't be bothered to fix this issues via regular free updates).

> I'm still having issues with reconnecting (after sleep, on startup, ...) to wifi on my air

The good news is that this cancer has spread to iOS 6 as well. I curse Apple every time it happens (on my Macs or iPad) and I have to open/close the lid again and again...

< 10.1.7 was all right. I don't know what they did that caused this behavior...

For the fans - SMCfan - http://www.macupdate.com/app/mac/23049/smcfancontrol

This seems to do the exact opposite of what I want (haven't tested it yet).

The description on the site is not so good, but you can set the speed to anything, for instance setting it at 2000rpm rather than the 4000rpm default or 6000rpm on high

There's "200+ New Features": http://www.apple.com/osx/whats-new/features.html

which is even more of a joke.