With WordPress 2.8 comes changes to XML-RPC, which is what lets you use external software to publish to your WordPress blog. Joseph Scott has outlined the changes, along with the ones made to AtomPub.
I did a quick test with MarsEdit and Blogo, two OS X blog applications I use on a semi-regular basis, and they work as normal. Has anyone had any issues with external applications after the 2.8 upgrade?

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Yes! I have!
The WordPress app for the iPhone won’t work with it, and Flickr can no longer “Blog This” to my (self-hosted) WP 2.8.1 blog.
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Images are not attached to the post anymore while posting with windows live writer.
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