I have made contact with people I had not seen or heard from in 30-40 years. People it was nice to hear from. Conversely, I've been approached by people I was glad I hadn't seen in 30-40 years. I have all my security stuff cranked down all the way. No one can see my page unless I allow it. And I only make friends with people who actually are my friends. It kind of violates a basic tenet: "Don't let too many know where you is." But, for the most part, it has been positive.
I don't think some people realize exactly who is reading their postings. So many times, something has come up on the screen and I've said, "Wish I didn't know that" and usually block the person. Other times, it gives the feeling like when you see someone yelling at their kids in the grocery store. Some people post *everything* they do: "Had a lovely cup of coffee today", "I had a completely divine bowel movement this morning. It left me with a feeling of....accomplishment!"
(tuba-geek aside: Makes me cringe watching people put shiny instruments down on concrete, stone, etc. Likewise with mouthpieces set on the rim on any surface... )