After some testing I have been able to write posts for my blog on my iPod, on the web, and in MacJournal. Anything that’s on the web site will sync down to the iPod, but MacJournal doesn’t seem to receive changes from the blog after downloading the initial blog post.
I’ll post on the macjournal forums to see if that’s normal or if it’s a bug. I’ve tried to download edited posts using macjournal 5.0.4 and 5.1.