Sticking to his article:
"Mail crashes all the time." "Fullscreen apps have a habit of just vanishing. They’re running, but they’re not showing." "Finder periodically decides you don’t need to see all your windows any more." "iTunes boot time is measured in aeons." "The “Something has crashed, send a report to Apple” window might as well be your Desktop Picture."
Happen to agree that Launchpad and Mission Control aren't great but that's just my personal opinion.
On both machines I upgraded from the previous OS.