(image source: Wikipedia)I suspect, though, that the traffic growth is more a tribute to our insatiable appetite for naughty pictures, bootleg videos and software, and passionate debates about atonal musicians than a testimonial to continued use of USENET as a social network for professionals.
I'm sure a lot of younger people think "social networks" started with MySpace and Facebook. For those of use who predate the Internet (yes, kids, a few of us remain), social networks were once both virtual and analog (cf. "Old Boy Network"). After the introduction of the Internet, but before the advent of the World Wide Web (second note to the kiddies: yes, the two are distinct, and came into being several years apart), we began to enjoy a new way of connecting with people outside our sphere of physical contact: bulletin boards systems (BBSes). These tended to be text only and slightly cumbersome, but they were for many of us the first medium for broadcast communication, where your message is not directed at a specific individual, unlike letters, telephone calls etc. (For me they were the second such medium; I was an amateur radio operator briefly in my teens.)
Then came the mother of all BBSes, USENET. I think it caught on first with system operators, programmers and other "computer geeks", then with a smattering of other technical types. (Bear in mind that, in the early days of the Internet, access was somewhat limited, largely to universities and the military here in the U.S.) Then came the flood of, um, less technical stuff (alt.animals.otters? alt.amazon-women.admirers??). Circa 1993, Mohan Sodhi came up with the idea for a USENET group for operations researchers, and sci.op-research was born.
For a while, at least, sci.op-research was a way for individuals in the O.R. community to ask and answer questions, and for the occasional non-O.R. person to get help. By 2009, Mike Trick was ready to pronounce it, and the rest of USENET, irrelevant. Today, sadly, it has little non-spam activity. (Mike gets the self-fulfilling prophecy award for creating OR-Exchange, which likely is the nail in sci.op-research's coffin.) Someone with a quick O.R. question or thought today may think Twitter first; for a longer question, they likely will look to a web forum (such as OR-Exchange). Google+ may yet become another viable alternative for communications with and among O.R. people.
Still, in its heyday sci.op-research (and at least portions of USENET) served a useful purpose ... and not just to let O.R. professionals network with each other. One time I answered a question from a practitioner (MS in some engineering discipline, no formal O.R. training that I recall) that led to an exchange of emails as we pinned down the answer to his question. A year later he contacted me again, offering co-authorship in a paper (which landed in a respectable journal). To this day I've never met my co-author. Neither the collaboration nor the paper would have happened without USENET.