10.8 is out. I have been playing with the Developer Previews and enjoyed the experience. Top of my list for worthwhile reasons to upgrade is Airplay to your TV via the Apple TV. The video mirroring will be only available to 2011 and new computers, but worth the convenience. Notification Center, Notes and Reminders are all there from iOS. Overall integration with iCloud is much cleaner and transparent. MobileMe syncing was flawed in so many aspects and I have not seen that to be so in iCloud, but time will tell. Overall it is a great update and at $19.99, if your computer and 3rd party apps support it, then go for it.