"If your account is less than a year old, please don't submit comments saying that HN is turning into Reddit. (It's a common semi-noob illusion.)" - http://ycombinator.com/newsguidelines.html
Not a really useful guideline. Just because my account is new doesn't mean I haven't been reading HN for awhile. I just never felt like commenting here.
Agreed, it's not a useful guideline. It's creating a truth out of thin air: "HN is not turning into Reddit."
EDIT: I'm getting downvoted for this but I think I'm bringing up a valid point. "HN is not turning into Reddit" is taken to be true a priori and the guidelines call for us not to question this. This seems to go counter to the general spirit of HN of allowing intelligent discussion and opposing points of view. (However, if a comment merely says "HN is turning into Reddit" it's not valuable; it should go into more detail and contribute something new and useful.)
No, it isn't. It's stating that claims that HN is turning into Reddit when authored specifically by people with newer accounts are less likely to be valuable. It's almost a direct corollary that long-term HN users have enough perspective that their complaints about the decline of HN's quality are at least potentially worthy of consideration.
Well, you're not bringing up a valid point. You see, HN is not turning into Reddit. The guideline is not creating a truth, it's stating a fact that has been true and remains true.