There are lots of interesting comments here.
However let us just for a moment restrict to ourselves. IT and other technical/STEM/whatever ladies and guys.
These days I expect anybody I hire in this sector to have at least a basic understanding of all the "everything on internet is public" stuff.
These days I expect anybody I hire in this sector to have at least a basic understanding of restrict access to your facebook (and similar) profile to friends if you don't consider those public including yang Tsu in China, Markus Hinterhuber in Germany and your next employer.
These days I expect anybody I hire in this sector to have at least a basic understanding of Linkedin is business, not personal. This means a profile picture appropriate for the kind of job you are looking for (bad vacation pic in swimming trunks is unexpected on a high level CV), a reasonable amount of spell and grammar checking and so on (as I said, calibrated to the kind of job).
If these don't match it doesn't mean I won't hire them, but it is an alarm sign compounding other impressions. AGAIN: CALIBRATED TO THE KIND OF JOB, now don't come and crucify me.