I just upgraded to OS X 10.11.2 (El Cap), and overall it seems to be working OK.
One strange thing: there's a "pkd" process which is taking ~150% CPU, all the time, even though I'm not doing anything.
(At first I thought it might have something to do with Spotlight reindexing or something, but 12 hours later it's still going.)
What is it? Can I stop it?