This release contains an important security update. Passwords
since 0.5 have been written straight into the log files without
filtering of any kind. This could enable a malicious user with
read permissions on the log files to discover other users'
passwords. We've repaired the problem in 0.6.1. It is
recommended that everyone upgrade immediately. You should
also delete production.log and development.log.

For a complete list of what's changed see:

http://dev.radiantcms.org/radiant/browser/trunk/radiant/CHANGELOG

To download go to:

http://radiantcms.org/download/