Another person on my friends list (several, actually) sometimes posts on LJ to call a Dim Sum outing. He just wants some people to come, not any specific individuals, and expects to sometimes be surprised by people he wouldn't have expected to respond. LJ is the perfect tool for that.
People write on LJ for a mostly consistent readership they expect to know, so unlike with most blogs, LJ writers often don't think about newcomers or casual surfers when they write. This can fail, too, because even the people you know haven't been there for every post since the beginning, usually. There are some people on my friendslist who sometimes talk about "BPAL". Presumably, at some point, this abbreviation was defined, but I've never seen it in the year or so since I've seen it being used. On most non-LJ blogs, an abbreviation like that would be explained in each post it's used in, but on LJ, how long do you go before filling your new readers in?
barmaidblog is a well-done hybrid: she writes in LJ style, but with a "typical" blog audience in mind. One of her adaptations for that audience is that every reference to a person or event she expects her readers to be familiar with, is a link the first time it appears in a post. Links lead back to earlier posts so new readers can drill back as far as they need to build up as much context as they want at the time.
( ... and then there's the classic case of "breakup via LJ" - I've seen a few of those ...)
What are some ways people you read use LiveJournal that don't quite work? Or that do work, in LJ-specific and interesting ways?