I used to be meh about hash cash style proof of work. Since listening to nostr:npub17u5dneh8qjp43ecfxr6u5e9sjamsmxyuekrg2nlxrrk6nj9rsyrqywt4tp recently I think it's integral to stopping spam (alongside web of trust, which is a subjective evaluation of content quality relative to the user as opposed to blanket domain reputation). Still have to build it though.