Weird. That's all I can say.
I don't know how well tested this update is, but judging by the tons of complaints, I'd say Apple have cut it loose maybe a bit too early.
I've installed it early yesterday and had almost no problems. The only real issues are more of a nuisance than problems - the update remapped my keyboard shortcuts to the defaults (where for some weird reason the shortcut for Spotlight and Input Source are both mapped to Command-Space) and now I can't turn the Bluetooth off. The latter really bugs me, because the Bluetooth is probably draining my friggin' battery.
Well, all in all the update is a great one for me, snappiness and everything, but Apple should try to find a way to test more thoroughly the complex monster of an operating system Mac OS X is.