I just can't imagine how spending one's time "tweeting" or maintaining a Facebook page has much to do with what kind of employee I want, unless perhaps those "tweets" particularly socially unacceptable.
If you don't have a facebook page (with friends...) the question of 'why not' arises. Do you not have any friends? Are you not allowed to use facebook? Sure, the Facebook privacy invasion service is well, a privacy invasion service, but if you can't connect with the vast real world of people who use it I have to wonder about how well you're going to get along with all of the other people on staff who aren't technical. I don't care how brilliant you are, if you can't get along with people I don't want you as an employee. If you haven't at least used twitter, or don't have a smartphone how tech savvy and current are you? Well.. if you just moved to this country and you don't have a job and don't have a cell phone then no big deal. If you have lived here for 5 years and don't have a smartphone I have to wonder about your nerd cred (depends on the job).
But why would I - why SHOULD I - give a shit about my applicant's "tweets" unless perhaps they deal with bizarre rape fantisies or something, in which case I might reasonably wonder why my applicant isn't smart enough to use an alias?
Yes exactly. If you're claiming to not be tweeting, are you tweeting under an alias that is going to come back and bite me, as the employer, in the ass when it gets found out? So you do care a lot about what people are doing online, especially if they aren't at least kind of open about it.
In other words, in my opinion, your "tweets" and Facebook prattle have no interest to me in terms of evaluating your job skills. In fact, I might be uncomfortable with someone who spends too much time in an on-line world.
You're contradicting yourself. You very much care. You don't care if it's normal and uninteresting. You care if it's abnormal. And you kinda want to find out which of those two bins the person is in.
If someone comes in for a job and you ask 'what are your 5 most frequented internet sites?' and they say 'I don't use the internet' you kinda wonder about them. If they say 'the pirate bay, torrentfreak, pornhub, redtube, tor, etc.' then they're a bit too honest. If they say 'network world, slashdot, reddit. facebook, google' then they at least know what a good answer is.