It's been two months since a new version of Joomla 1.5 hit the streets, and not a moment too late. The new release has the longest change log we've seen in a long time, including some high priority security issues and dozens of bug fixes and changes.
The Joomla proclaims Joomla 1.5.9 is "a security release and users are strongly encouraged to upgrade immediately." So get to it!