Recently I had an exchange with a work colleague about Facebook - she'd seen me listed as "People you may know", and I'd seen here there too. A new etiquette issue of our times is whether "friending" someone on Facebook means crossing over from their professional life into their personal one, and whether that is an issue for them. So neither of us had yet clicked the "Friending button". This is to do with my earlier theme of how Facebook and the like can break down the Chinese walls we like to have in our lives.
Some people mix their work and leisure circles freely on Facebook an its equivalents, others like to keep things separate. You can't tell before clicking "Friend" which camp this particular person is in (unless a person has set their Facebook privacy so that everyone can see what they do there, and there are good reasons you might not want to do that) .
My own practice is that LinkedIn, Twitter and this blog are where I publish my professional life, whereas my Facebook posts are about my hobbies, sometimes about my family, and about my sense of humour. Judged from my facebook account, I do not work at all: at least I rarely if ever discuss it.
That creates a stream that I don't mind people from my professional life seeing, but that I recognize will be utterly uninteresting to many of them. So I tend not to friend. It is not that there is anything on Facebook that professional colleagues should not see. I assume that posting on Facebook is Publishing - there is every chance that current or future clients will get to see it, so it is not the place for innermost secrets. But I don't want to bore. My professional and facebook networks DO overlap of course, but either with people who have "friended" me (I'm unlikely to turn down anyone I really know) or where I know, from non-work time with people (watercooler, lunches, pub etc.) that they aren't likely to mind exposure to my leisure interests.Or sene of humour. I don't see Facebook as an Inner Circle to which only special colleagues get promoted, just a different circle of people with a high tollerance of my leisure interests.
(Speaking of Circles, I am on that too, but have yet to take the time to understand it. Until then, I'm keeping quiet on it).
So - if you are a professional colleague of mine, see me as a "person you might know" on Facebook and are wondering whether to "friend" perhaps this will help you decide. If you are wondering why I don't "friend" you, this is probably the answer (i.e. nothing personal).