Turns out there's a working Java 6 for both Mac OS X Tiger and Leopard. It is a port of the Java Research License licensed codebase for BSD, so to use it legally, you need to agree to JRL first. It's developed by a person named Landon Fuller, and he says on the page:
The Mac OS X work is based heavily on the BSD Java port, which is licensed under the JRL. The BSDs develop Java under the JRL; FreeBSD has negotiated a license with Sun to distribute FreeBSD Java binaries based on the JRL sources.
As the Mac port stabilizes, I am merging my work upstream into the BSD port, and in turn, it is a goal of the FreeBSD Java project to merge their work into OpenJDK. I've signed a Sun Contributor Agreement in preparation for this...
There are some minor features lacking (minor if you're like me, using Java for server side): sound doesn't work yet, nor is there a native Aqua Swing UI.
Via Charlie Nutter (who also perftested it with JRuby and sounds quite impressed).