Hey, For me, there's a noticeable difference in responsiveness between Mavericks and Yosemite. This with the integrated Intel graphics card. If I force the system to use the Nvidia card, everything becomes very smooth in Yosemite. However, everything WAS very smooth using the integrated Intel card in Mavericks. But now, in Yosemite, changing between spaces, opening Mission Control etc seem to lag a bit. It's not a lot, I think not everyone might notice it, but I do. And between Intel and Nvidia there's in my opinion a noticeable difference in smoothness. Is Yosemite just a more resource intensive OS?