The frequent Yosemite beachballs seem to only occur on systems with old-school hard drives. It's nowhere near as bad on SSD systems. It's crazy frustrating on my iMac, but my macbook pro is fine.
So I suspect the changes and additional daemons in Yosemite added a bunch of disk I/O, and the engineers never noticed because they're all on SSD systems.
So I suspect the changes and additional daemons in Yosemite added a bunch of disk I/O, and the engineers never noticed because they're all on SSD systems.