Following are provisional guidelines for what's roughly appropriate for each of our sections, and some short examples of how to decide where new stories should be posted. These guidelines apply to all authors and editors (which, potentially, includes everybody using the site!), and will hopefully be informative to casual readers as well.
First of all, most everything on the site needs to be in scope (be sure to read the rest of the faq while you're there :). The main exception to this rule is Diaries, although even there we hope you occasionally mention something relevant to your hackery/librariany lifestyle.
Second, if you think stories need to be moved around, try to at least post an editorial comment with your thoughts (editorial comments include any comments posted while a story is still on the moderation queue, and appear framed in red to users looking at all comments). That way if an author is confused or agitated about why the story they posted landed somewhere other than the section they posted it to, there's at least some basis for discussion and a record of what happened and why.
Finally, the broadest rule that applies everywhere is to be considerate. We want to create a friendly space here, and we will not hesitate to block users who wantonly step on that mood.
When is a story not a story?
Basically, if what you're posting is a link to a new issue of some in-scope ejournal, or a handy software tutorial, or anything that's really being published elsewhere, _and_ you're not really adding any value to the link beyond an informative title, a brief comment, and maybe another context link or two, what you're posting is MLP. That's not to say that's bad, or that we don't want MLP! In fact we love MLP... as long as it's in scope. There are plenty of related weblogs out there, though, so we want to focus on filling our sections with original work; pointers are welcome, but they should go in MLP to keep the other sections clean, and so all the MLP be reviewed in a quick scan. That's what it's for, after all. :)
On the other hand, if you're linking to such a piece and adding substantial (at least more than a few sentences) and original (not just quoting somebody else!) comments analyzing what's there critically, or providing missing backstory, etc., you're probably posting a new story, and it should go into one of the topical sections.
What goes in which topical sections?
Any substantial (i.e. not MLP) new story that largely reports the who/what/where/when/why of something that's in scope but doesn't fit in the other topics. An example: "Such and Such Company Buys Some Other Company We Care About in Libraries" with some analysis.
Original pieces exploring some issue, person, event, or problem relevant to hackerdom/librianship. An example: "A New Approach to Solving the Broken URL Problem". This would be a good section to post early sketches for pieces you might want to work into a formal publication down the road -- you'll get some early feedback which will (hopefully!) help round your work into shape.
Stories which go into some depth about a using some piece of software of interest to our readers (e.g. SiteSearch), or integrating a few applications together, or approaches to dealing with paradigm impedance (e.g. object/relational, data/document, etc.), or architectures, or broader issues relating to the administration of software over the long term. An example: "Maintaining an Integrated Search Interface at U of Zyxw." Or maybe "Which EReserves Tool Should We Use?"
Pointers to events (conferences, workshops, etc.) in scope, including previews, trip reports, reviews of talks, etc. An example: "LITA/OSS Preconference Workshop at ALA Annual." Be sure to include dates, times, places, etc., and link to the appropriate event host's page if appropriate.
Stories covering advances in formal work developing standards in scope, or critical analyses thereof. An example: "NISO Committee developing XYZ Standard Publishes Updated Draft".
A la Ask Slashdot, post questions here about how to solve library/tech problems, or help making choices, etc. An example: "Which programming language should I learn?"
Any pieces which cover topics that are in scope but are explicitly your own commentary, pro or con. An example: "Why Digitization should be Considered Harmful".
The only guidelines here: diaries are not moderated... what you post goes online. Site administrators can remove inappropriate diary entries, but we really don't want to have to. Remember: don't post anything you wouldn't want all of us to read. :)