Joomla 1.7.3 and Joomla 1.5.25 were released today, as a result of a zero-day security issue. Because of the security issue, it’s recommended that you update your sites immediately.
Joomla 1.7.3 fixed 77 CMS bugs as well as the two security issues.
One of the big new features in Joomla 1.7.3 has to do with multi-language improvements, which are summarized in this blog post.