Mac Rumors, on the most recent developer build of the next update to Leopard:
As with numerous previous developer builds, the inability to install Safari 4 Beta remains the only documented issue. Development on OS X 10.5.7 has been presumed to be wrapping up for several weeks now, but Apple appears to still be finding a few bugs that require their continued attention. The last developer release, Build 9J56, was seeded in the middle of last week.
The current release of Mac OS X (10.5.6) was released in December - over 5 months ago. With such a long wait, I’m starting to think that 10.5.7 may be the last major update to 10.5 we’ll see before 10.6 comes out.