Dave,
LinkedIn is an interesting community of sorts: each person may place their profile there, ostensibly so they can "network" with others and either get a better job, or get work (if they consult). It is also an insurance policy of sorts if you find yourself in a RIF...
I have been "invited" to join in for one of my daughters, and others I know (in all sorts of different fields, completely unrelated to my field).
Since I have no need to advertise myself (just google "Austin Lesea"), I find it something next to useless (for me).
Being of a totally different generation (the last of the baby boomers), I am not all that excited about any on-line community (I prefer real community, with a good Cabernet, or Pinot Noir).
None the less, this is a sort of 'FaceBook' for people with a professional job (or looking for one).
Just like any other on-line experience, we will see if it is successful or not. My guess? With the price of gas, meeting on-line gets very attractive. Working from home once a week is now something the government is thinking of legislating...(more laws=bad government, I'm afraid. Let the market decide is my view).
Although, I would easily drive 40 miles if a glass of good wine is involved. More if the people are my friends, too.
On a completely different topic, this weekend will be the 44th year of the "Chews Ridge Gang" for ARRL Field Day...wish us luck -- we will need it as most of Northern California is on fire, and still burning (so we may not have access to Chews).
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And, upon reflection, my "on the air" community is a lot more fun than the Internet.
Austin