From time to time MarsEdit users ask whether there is or will be any support in the application for “automatic crossposting.” While MarsEdit is great for managing multiple blogs from a single interface, it still requires you to manually open separate windows and “send” the post to each of the blogs you want to publish it on. Some users would like to be able to define a “metablog” in MarsEdit and have posts to that destination simulcast to multiple blogs.
I’m hesitant to change the MarsEdit interface to support crossposting more automatically, because I think it would be to the detriment of users who use it for more conventional purposes. But future development plans might make it possible to support crossposting as a “scripted action” that runs whenever you publish to a particular blog.
In the mean time, a great solution is to rig something up on your weblog server. In particular, I know of one plugin for WordPress that automates the process of crossposting from WordPress to LiveJournal. For more details about how this works, see the recent entry from Tycho about his use of the plugin in conjuction with a WordPress blog and LiveJournal.