Good questions, thanks. SE is an abbreviation for single-ended, which means the amplifier is running in Class A mode. SET is single ended triode. The boxes by each participants name show the IP address of the sender. Older posts were hosted on a different webserver and had a slightly different layout.As for what's on-topic and what's off-topic, each forum has a link at the top for "rules" that tells what what's cool and what isn't. Generally, the open forum topics are limited to what the forum name describes, but it ain't a sin to drift a little bit. Except in the Tower and the Dungeon, long arguments about politics or religion are frowned on, but a little drift isn't bad. Sponsored forums are a different story - They're basically what the sponsoring organization wants them to be, and are usually support forums.
Here, as long as a post isn't rude or aggressively self-promotional, it is usually allowed to stand. It's sort of like a club - We don't throw anyone out unless they get too annoying, and that pretty much sums up the rules here. But on the open forums, the rules are a little more articulated than that.