Good question, as politicians are wont to say.What is a "serious shaver"?
That's purely subjective, though I figure that people who take the time to post photos and/or descriptions in "SOTD" fairly regularly are relatively serious about their shaving. This, of course, is not to exclude people who don't post.
As for what constitutes a "serious shaver" beyond posting in "SOTD," I'd say membership in B&B itself. There's a measure of eccentricity here: many of us compare blades and razors; we rate soaps and creams; and debate the merits of aftershaves and fragrances. This is not your usual dinner table talk.
Also, note the word "serious," as opposed to, say, "expert." I've been shaving since the days of blue blades, but I'm by no means an expert at anything, let alone shaving. Nonetheless, I am a bit more serious about my shaving than the average fellow who shaves with cartridges and foam--and who might find the goings-on here rather quaint and ridiculous.