Hi there! I've just installed last yosemite beta for curiosity, coming from mountain lion (i didn't switch to mavericks). I've noticed an overall slower response of the system, especially in finder operations (it seems about 0.5 second slower than mountain lion). Also when reading a big pdf file in preview there is often lag when scrolling down/up. These performance issues could be related to the fact that i am on a late 2011 macbookpro and yosemite is optimized for latest hardware mbps? Or because it is still in beta? I am a bit disappointed because it seems to me that yosemite is quite less responsive than mountain lion in standard operations like open/close folders/files, open/close web pages etc..