Hi, How can this be possible, since everyone says Mavericks performs better? My MacBook Pro Late 2009 has 4 Gigs RAM and two HDs (1 SSD and one 7200 RPM), and I performed either an upgrade from ML, and a second time a total wipe of the hard drive and install of Mavericks from zero. In both cases, I experience a better behaviour of ML over Mavericks: snappier transitions, more fluid video streamings (i.e. SkyGo), Mac goes to sleep almost istantaneoulsy (on Mavericks it takes more than 10 seconds), no app crashes, fan turns on less often... I don't use finder so there's no indexing, by the way no improvement over a month; Mavericks behaviour improved with 10.9.1, but in any case using ML over Mavericks is like having an iPhone over an Android. Even web page scrolling is more fluid with Mountain Lion, no hangs at all... so I decided to go back in order to have a better experience. But I suspect there's something wrong, I can't understand: maybe my hardware is too old to gain the better performance given by Mavericks; surely ML is the best OS for my Mac, even better than Snow Leopard, the original OS. Anyone having those kind of experiences?