"Pick out particular snippets" seems to work quite well. If something in the topic of conversation tags, in my mind, to something I read on LessWrong, I usually bring it up and add it to the conversation, and my friends usually find it neat. But except with a few select people (and I know exactly who they are) posting an article on their facebook wall and writing "this is really cool!" doesn't lead to the article actually being read. Or at least they don't tell me about reading it.
If facebook is like twitter in that regard, I mostly wouldn't expect you to get feedback about an article having been read - but I'd also not expect an especially high probability that the intended person actually read it, either. What I meant was more along the lines of emailing/IMing them individually with the relevant link. (Obviously this doesn't work too well if you know a whole lot of people who you think should read a particular article. I can't advise about that situation - my social circle is too small for me to run into it.)
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
If continuing the discussion becomes impractical, that means you win at open threads; a celebratory top-level post on the topic is traditional.