IAAL. Don't go too far thinking that existence of a trademark depends on whether you see a (TM) or (R). The touchstone of trademark law is whether your branding will make customers think you're related to someone who was in the space before you. If you're confusing customers, you have a problem; if you're not, you don't. Having an (R) makes it easier for the earlier entrant to prove infringement and collect damages, but it's not the end of the story.
(So for example in this case, when you say that the number of sites using the term Hacker News invalidates the trademark, what you mean is that no reasonable customer would think Paul Graham sponsors HNM, because the term Hacker News isn't associated with this site in particular. That's, let's say, up for debate.)
Trademark is actually one of the sanest areas of IP. It's pretty much about whether the alleged infringer is hurting consumers or not. I've fantasized sometimes about what would happen if you applied the same principle to patent or copyright ...
[Disclaimer: This is so not legal advice. Don't be an idiot.]
(So for example in this case, when you say that the number of sites using the term Hacker News invalidates the trademark, what you mean is that no reasonable customer would think Paul Graham sponsors HNM, because the term Hacker News isn't associated with this site in particular. That's, let's say, up for debate.)
Trademark is actually one of the sanest areas of IP. It's pretty much about whether the alleged infringer is hurting consumers or not. I've fantasized sometimes about what would happen if you applied the same principle to patent or copyright ...
[Disclaimer: This is so not legal advice. Don't be an idiot.]