MarsEdit 1.0b4 can be downloaded from the MarsEdit home page.
Here are the change notes.
The goal of this release was to fix a couple high-priority bugs: 1) the bug with applying default settings when you choose post-to-weblog in another app and 2) sending trackbacks.
Some of you are eager for Markdown preview support and for customizing the list of sites to ping. Both of those features are still on the to-do list for 1.0, but theyâ€™re not in this beta.
WordPress is kind of a special case, since its external weblog editor support is a work-in-progress. (Make no mistake: I think WordPress is fantastic software, and I recognize that theyâ€™re working on fixing bugs with external editor support.)
So when we say that you can send trackbacks now, Iâ€™m not actually sure that it works with WordPress yet. It mightâ€”or, it might work with some versions and not others.