According to the most recent seed notes at HMBT.org, Apple may be trying to wrap up development of Mac OS X 10.5.6.
The latest Mac OS X 10.5.6 seed (9G38) provided to developers today lists no remaining issues. It's always difficult to predict when Apple plans on delivering the final version to end users, but having no known issues is usually considered a sign of pending release. The previous seed was published just earlier this week.
Again, Apple appears to be focusing on MobileMe sync testing for portable computers. In addition 98 other bug fixes are detailed within the published seed notes. Apple released the last update to Mac OS X 10.5 in September.