The RSS supported built into WordPress makes it easy to write a post in one place and have it appear in other places like FaceBook and Twitter. FaceBook automatically generates multiple RSS feeds based on categories and/or tags, so you can get as fancy with this as you want. For example, you can create a tag “FaceBook” and then have only those posts tagged “FaceBook” appear on your FaceBook.
To enable your WordPress posts to appear in you FaceBook stream, simply configure Account -> Application Settings -> Notes and select “Import my blog” on facebook and point it to your WordPress blog URL. If you just list the blog URL you will get all posts. Alternatively you can use the URL to a specific category or tag.
To keep the size of the post fed to FaceBook reasonable, set your WordPress reading settings “For each article in a feed, show:” to “Summary”.