Canonicalize URLs: at the moment, there are several different URLs referring to most pieces of content on Less Wrong. Sometimes it's as simple as one URL having a slash at the end and the other one not; in other cases you have a post that was actually posted in Discussion, but due to (I think) a glitch where Discussion posts as listed on userpages actually link to the post via /lw instead of /r/discussion/lw, and the former works anyway, causing two copies to be indexed in search engines, and the same for every comment posted on them. Preferably, every such piece of content would have a canonical URL, and any other valid means of accessing it should redirect to the canonical form via FOUND or MOVED PERMANENTLY, or at least specify the preferred URLs to search engines via <link rel="canonical">.