Short & Sweet Version
Love it. Works great. A couple of the new features only work with mid-2011 Macs or newer OR with SSD internal drives (i.e. Airs or the new Retina MBPro), but still easily worth the $20 to upgrade. No compatibility issues so far with my existing apps. You may have to turn off the new Gatekeeper security feature for a month or so if any of your existing apps aren't "signed". But I only had 1 and they quickly updated the app to be signed... So I've already turned the Gatekeeper feature back on. A lot of the iCloud stuff will really become even more useful once you update your iPhone/iPad/iPod Touch devices to iOS 6 in the fall.
Be sure and get a Time Machine backup or other HD cloning app to backup your Mac before you upgrade - just in case. You may find that an app is incompatible or run into an issue w/ the upgrade itself...although very unlikely.
And extremely important to note is the upgrade process:
- Go to Mac App Store in Lion.
- Click buy now button for Mountain Lion and type in password.
- After download, click OK to close existing apps and reboot.
- Wait a few mins for upgrade & reboot.
- Enjoy Mountain Lion.
