When did you become aware of/interested in various personality theories?
When I was about fourteen. My dad introduced me to the Enneagram. I then found my way to MBTI without his help shortly after, and then to socionics quite recently (within half a year).
Besides the aforementioned theories above, I like studying Oldham and Keirsey, and the less well-known systems.
How and/or why did you become interested?
I've always had a long running interest in studying people, and in introspection. It provides me with a lot of satisfaction for some reason. It could be to do with managing to compartmentalise everyone into sixteen, nine or more different types, or that could just be a side effect. I think what's more appealing is that there's a myriad of theories that can be used to my advantage.
What are your opinions (in summary, I suppose) of these theories?
I've always put my faith in their correctness. I rarely doubt their questionability. It's a case of building up my knowledge base, and then, if two things conflict, being able to distinguish between the good quality, well thought out system, and the bad one.
Specifically, I think socionics is the most logical, and I prefer it over MBTT. However, I still like discussing MBTT for purely intellectual stimulation. Type theory isn't as important, but it's fun trying to find out your own type, and helping others try to find theirs. I expect a lot of people feel like this. Keirsey and Oldham I like reading about and correlating with the different types. Enneagram has been my oldest interest. I refuse to believe that people do not have one of nine basic motivations, and one alone. I've encountered people who are either difficult to type, or who pretty much refuse to fit themselves into a type, but I believe they're confused, rebellious or simply disinterested. Even deep similarity between two types can be remedied; even if one says "I know I am both", they will have a base motivation.
I think I derive most interest out of those theories with a practical value. The Enneagram and socionics have practical value in my eyes. Keirsey does to some extent. Although I may not use the theories to their full capacity, I generally enjoy studying them.
When did you join a forum, mailing-list, or other such thing?
I've been joining them since I joined EIDB in 2006 I think.
I've tend to join ever forum on personality theory that is remotely active. As of yet, I haven't found an Oldham one. But I'm a member of similarminds.com, personalityzone.com, socionics.com, socionix.com, the16types.info, EIDB and this one. I also signed up at Dave's Enneagram Community, and continued to check for about two days, then gave up.
How and/or why did you become interested?
I thought that since I was so into personality systems, instead of blathering on to people who, quite frankly, couldn't care less, I should find some place to discuss what I thought about each theory. Forums are the best way of meeting likeminded people.
Were you an "active" member?
Currently, I'm an active member of this site, EIDB and The16Types. I stopped posting at the rest of them because they were either boring, unproductive or inactive.
Which one(s) do you use most often now?
The ones I'm active at.