I'm currently using mavericks. My MacBook got 2 hours of extra battery. The ram management is amazing. The system is faster...
Personally, as a Mac desktop user, that won't be a plus for me, however that's an amazing improvement in battery life and could certainly be worth the upgrade for that reason alone for people who own laptops. That seems to be have been the difference between Apple and MS over the years. While MS added more and more (some would say) often useless features to Windoze I'm a big fan of sorting out the really important things in an OS. Stability, performance, throughput etc. Should always be top of the list.
Unfortunately my first generation white MacBook (still going strong, albeit with a new battery) won't run anything later than Snow Leopard.