The latest operating system for Mac laptops and iMacs is now available. Price for the upgrade is $20.
Several articles describe the new features in OS/X 10.8.
And here's a review that focuses on the little details of Mountain Lion
All the reviews say the upgrade is worth doing. Significant speed improvements to Safari and better integration of iCloud network features top my list of reasons to get 10.8.
That said, I suggest holding off for a few weeks. There always are bugs and mistakes in a new version of any software, more so in a major release to your OS. I'll wait for version 10.8.1.