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?
Thord Daniel Hedengren is a designer, writer, and blogger, and also the former editor of The Blog Herald. He used to be a hotshot in the gaming industry in Sweden, but sold everything and went International. Most recently he wrote a book called Smashing WordPress: Beyond the Blog, and does loads of kickass design.