Get it now.
This is the fourth beta. There are various fixes in a lot of areas. There are some text editing fixes and some fixes for smart journals. There is now native support for importing OPML (outline) files. There are some various other fixes as well that are detailed in the Version History. There aren't any new features as 5.1 is feature complete already. Providing localizations is also a goal for this release, although none are included yet. Please let me know if you have any problems with this beta.