Speaking generally about "the Internet", I've had several pseudonyms, many of long-standing use and some of considerable reputation.
I haven't been... "paranoid" about my identity, and several to many people have ended up knowing the formal identity behind the pseudonym. But that has been at my own or our mutual discretion.
I chose the words "formal identity" because, even while using a pseudonym, I feel people can and do come to know my... "real" identity. What I think and feel and communicate, regardless of the ostensible name attached. I usually take some considerable care in my communication. My use of a pseudonym doesn't, in that regard, hide who I am.
What a pseudonym does let me do is dissociate certain contexts.
I can be a little more open about some past work experiences, here, because they don't "pop to the top" upon googling my "real" name. Not that I'm engaging in slander or criticism verging towards abuse. Mostly, I'm also circumspect about not identifying the other party (e.g employer). I wish to be able to be fairly honest and open about communicating my experience and thoughts upon same, without having to worry about this raising concern with a current or future employer. Or... these days, without having to worry about some draconian policy or attitude surprising me with e.g. a SLAPP lawsuit or similar.
Rather than picking on particular people or organizations, there are experiences that have taught me things. Sometimes, things I wish I could have learned a bit more easily and/or sooner. If I can save the next person a bit or grief, or help them to be a bit happier, then yay! A pseudonym helps me to go about that without second-guessing every sentence.
In another instance (and another pseudonym), I've dealt with concerns that run from "personal" through "health". Many people online find much value communicating about such matters in an anonymous or pseudonymous context. Again, it's about the content, not about the who. I've witnessed and experienced many significant relationships develop and persist in such pseudonymous contexts. Some people establish additional private channels and may or may not share identifying information. But, as I've observed, it's not necessary.
And, that brings me to a favorite phrase and attitude of mine, with regard to online communication and to many aspects of technology, as well:
Opt in.
I'm a strong believer of letting people opt in to choices, such as whether or not to share personally identifying information.
If per the meme the Internet or the Web is today's "Wild West", then I'll borrow another analogy, or component of this Western mythology and attitude (the attitude part is significantly true, even today): It's not who you are, it's what you do.
Per the Western genre of story, the West was somewhere a person could "reinvent" themselves. It's not who you are, but what you do.
On the Internet, I don't think we really "reinvent" ourselves. But, it is a matter of what we do, rather than who we are.
Perhaps that's one reason I'm a bit cautious about the influx of photos and other imagery. I get enough of that in... "meatspace", as I guess it's sometimes being called, these days. "Real life".
People who succeed to varying degrees on their looks and other external factors.
Some days, give me pseudonyms and plain text. Or code, or the like. And show me what you think and do. Even what you feel -- I've seen as much genuine empathy and feeling on a phpBB forum as anywhere else.
So... to go a bit beyond the clicky-votey spot above...