I also find it ends up looking rather spammy. A blog article is written, and then it's posted everywhere in an attempt to drive traffic to it. It's often hard to see a difference between someone practicing POSSE and someone spamming in an attempt to help their SEO. This is especially true of 100% of their posts are just links off to the blog, where they treat all the social platforms like alternate RSS protocols.

A social networking site designed around POSSE may be different, where you can subscribed to your blog as a means to post, and the post shows up as the RSS would in a feed reader. This way people don't have to click through to read what was posted, or can at least read what is above the fold. This can be rounded out with comments, one-off posting, and maybe some standard way to write a blog post that references another, for a proper linked/threaded response for more thought out and thoughtful replies than a short comment.