Mountain Lion, while a very stable and worthwhile upgrade for its various under-the-hood benefits, did have one problem: in many cases, it noticeably reduced the battery life of most notebooks. 10.8.1 helped with this problem, though only in certain limited cases: for many, the issue remains.
Apple has been releasing 10.8.2 beta builds to developers since late August – two days ago, it released the third beta. This third beta fixes many issues, adds features such as Facebook integration, but also has a significant improvement in the battery life department, taking it to levels even surpassing that of 10.6.8, Snow Leopard’s most stable build.
These results were found by The Mac Observer, and they note that it seems a fairly regular pattern that new releases of OS X have a negative effect on battery life, while subsequent updates have a positive and noticeable improvement.
Personally, running 10.8.2, my battery life woes (which actually only appeared after updating to 10.8.1) seem to be cured. Mountain Lion has so far proved to be my favorite release of OS X, surpassing even Snow Leopard in both stability, speed, and now battery life.