This is the first beta of 5.1. The goal of this release is to provide a few larger features, a few smaller features, and provide localizations. We are currently working on the localizations so there are none in this release, but we will use this as a reference point and update what we have. This release is feature complete, which means I don't plan on adding any new features, largely because of the localization issue.
The big new features in this release is an option to have the entries list display vertically on either side of the entry text, enhancements to the calendar to support non-Gregorian calendars and display more than one month at a time, and editable entry windows. I also added Karelia's Media browser to see pictures and so forth from iLife applications and drag them in easily. There are a few other improvements and bug fixes, so I encourage you to read the Release Notes and the Version History for this release. You can go back and forth between this release and the last public release, 5.0.4, without any trouble. As with anything, it's a good idea to make backups before changing just about anything on your computer though.
Get MacJournal 5.1b1.