Apple has posted a release of JDK 1.5 (MacOS X 10.4 only) on the support site. Once installed, this release does not become the default Java runtime (1.4 remains the default). This is interesting, as is the paucity of documentation for the release.

[update] Upon actually looking for some documentation, I found release notes, Apple extension docs, and an intro guide updated for JDK 1.5. Good stuff.

[update #2] The performance of the 1.5 build is pretty good, but there appear to be some bugs in Swing.