Get it here.
This beta has some bug fixes and improvements in behavior. It also should improve behavior when facing conflicts with data on Dropbox since Dropbox has its own way of handling conflicts. Other than that, large images should look better in certain WordPress templates, the default auto-save time is now shorter, most of the items in the Text Cleanup menu will work in the Topic field, and double-clicking an entry with content that can't be edited in MacJournal directly will open the best application for that content directly.
Please let me know of any issues that you have via the Report a Bug item in the Help menu.