I had real problems with the update. No Finder, no Dock, no HD avaialble on the desktop. Hard restart, then abandoned it & went off to use my son's Macbook (without updating it!). Half an hour later my iMac started working again, though sluggish, with the spinning beachball working overtime. Haven't even dared to open Aperture yet. Normality seems to be breaking out slowly, though I've done nothing more than check emails & use Safari so far.
My advice - proceed with caution