I'm pretty sure most of y'all regular readers know this, but I figure it can't hurt to say it again every now and then, just in case new people wander through.
Every now and then, for various reasons, I Google for an author's name and the title of the story they've just submitted to us.
And a remarkable percentage of the time when I do that, I discover that the author has previously posted the story, in full, on some website. Occasionally it's an online magazine of some sort, whether non-paying or semipro (and in those cases the author really ought to have known better than to send us a reprint without telling us it's a reprint), but more often it's just on the author's LiveJournal, or on any of various sites dedicated to allowing people to freely post their own work publicly.
And unfortunately, we can't consider unsolicited work that's been previously published elsewhere--and, like most sf prozine editors these days, we consider any appearance on a publicly accessible web page to count as publication.
So unfortunately, if you post your latest story in a non-friendslocked blog or LJ entry, you may be making it difficult or impossible to get an sf editor to pay you to publish that story later. No matter how few people read your LJ. (Editors in other fields may feel differently about this; the only editors I've heard weigh in on this question are sf editors.)
So if you're interested in selling your work to a professional sf venue, I strongly recommend that you not post it in a publicly accessible place online.
(Note that posting it for a while and then taking it down when you're ready to submit it is also a bad idea. If it's ever appeared publicly online, we consider it to have been published, whether or not it's currently available online.)
There are all sorts of tricky corner cases to this issue. We at SH are currently taking the position that if a story is password-protected (not accessible to the general public without some kind of logging-in process), then that doesn't count as publication (except in cases where it's clearly intended as publication, like if you sell the story to an online venue that password-protects its content, as some do). Other editors may draw the line in other places.
But at the very least, if you feel you must post your story in your LJ, you should friendslock the post.