I've installed Lion on my iMac (24-inch, Early 2008, 3.06GHz Intel Core 2 Duo, 4GB RAM) and it has become INCREDIBLY slow. I've heard many people saying that the machine would return to its typical blazing speeds after indexing finished, and it has — I've left it on overnight a couple of times to make sure everything finished, and it's still much slower than it was while running Snow Leopard. Virtually every application hangs — when typing in Finder (for example to rename a folder) the text lags several seconds behind what I'm typing. Mission Control is terrible — the graphics lag behind and it takes several seconds for the animation to finish. Often the animation doesn't appear at all, and it just flickers between frames awkwardly until the mission control display finally appears.
I'm working on backing up all my data and doing a clean install … I'll see what happens, but if it doesn't work I'm going to have to roll back to snow leopard, because this is ridiculous. I've never seen an OS change slow down a machine so much since Vista … hopefully it's fixable. Any thoughts on what might be the cause?
(Oh, and activity monitor scans look normal … nothing's hogging the CPU, and there's slightly less than 2GB of RAM free almost all the time.)
Thanks for the responses, everyone. I found disk permissions errors as well, but I will never know if that was the problem since I had already transferred all of my data off my machine to do a clean install, so I took that route anyway. The clean install fixed EVERYTHING! My machine is smoother than ever now. If none of the above works, install from scratch using a DVD with Lion on it (you can find instructions on how to burn a Lion DVD virtually anywhere now) and your problems should disappear. Enjoy Lion