Since late 2005 I think, but I didn’t use it for a year after.
I like it. it’s different from Forums, BBS’, Usenet or Chatrooms but not a whole lot different.
It took some adjusting to get used to the likes being counted; that changed my behavior in that way, probably for the better as I used to spam-like – which I still do in other more old-fashioned places.
And the AI sorting of posts was annoying at first but now I toy with it and try to coax it to do things for me and I like it.
I think of it like owning a pet. And no, I don’t feel owned by the pet. It’s my pet but it has a mind of its own.