I like tying it to karma rather than user date length. That way, long-time users that haven't done anything will still see the guidelines, as a sort of hint.

Why would long-time users that "haven't done anything" need the hint?

One may still benefit greatly from the experience of posting and commenting rather than observing. I was reading hn a while before I got an account, and never really thought about karma, submission titling or type, or comment voting.

I have often wondered why the posting, submission, and voting guidelines haven't been more prominent. I appreciate Paul's active role in this community--I think it account's for much of the civility to have benevolent moderators--but definitely making the principles easier to access would be helpful, too.

Incidentally, having the page detailing the post-formatting capabilities on the Reply page would be handy, so people are aware of italics,

  code indentation

and so on.

Yes, please. It took me a while to figure out how to indent code.

FYI, text surrounded by asterisks (*) will be intended. Begin a new line with two spaces, and you have code indentation.