Ok, I get it: yearly OS updates, and thus yearly decrease of overall OS responsiveness that forces me to upgrade machine every two or three years if I want to keep a lag-free system. iOS 8 much slowed down my iPad mini compared to iOS7. And the same has now happened on my mid 2011 iMac once upgraded to Yosemite. The computer is USABLE, but just desn't have the same responsiveness of Mavericks. Everything was perfect on Mavericks. Safari is now much slower. Opening and reordering tabs, slower, laggy. Everything in the finder has a laggy feel. It could be worse, but definitely slowed than Mavericks. I suppose the new interface is more resource intensive. And that's stupid. Aside from forcing you to upgrade your machine, why would they do that? Anyhow, my questions are 2: 1) The slowdown seems to be mainly on graphic operations: finder tabs, Safari tabs, launchpad etc. Are there tips to avoid the slowdown? Disabling effects, transparencies, shadows etc? 2) the slowdown in normal conditions is not too terrible, but yesterday I don't know what happened that made everything extremely slow. This regularly happens on my old Macbook Pro, which I am afraid to upgrade to Yosemite as Mavericks already made it way less responsive. But now this is beginning to happen on the iMac. Some application or something makes the Finder and opening Launchpad lag, to frustrating levels. Only restarting the machine cures it. Maybe question number two needs more info to be solved, I would have to go to Activity Monitor and so on. But I didn't really do anything special except using Safari, and opening and closing Adobe apps. There are no special extra processes in the background, I also use CleanMyMac2. Maybe there is a quick something to do to avoid forcing me to restart the Mac? I also have a FusionDrive...I am used to everything being quick and responsive, but Yosemite as expected lowered the overall performance and now I get those slowdowns too that I never gotten with Mavericks on the iMac. As I develop iOS apps, I am forced to always have the latest OS with the lastest SDKs. I guess that means I just can't use a few years old computers... No money to by a new desktop now, how do I make Yosemite speedy on the iMac?