Hmm, I just upgraded my MacBook Pro to Leopard. Everything seems to work fine so far, haven't tested much yet though.
What I can see in Java department is kinda weird:
1.3 folders remain, but this version can't be invoked directly as before. Will not be missed by many I guess.
1.4 was updated to the latest 1.4.2_16
1.5 was updated to the latest 1.5.0_13 as reported earlier
1.6 folders are present on my machine, but this version crashes, identifying itself as 1.6.0-b88-17-release. This was the last developer preview build from Sep 2006 that I installed on Tiger previously. Folder dates on my system indicate that 1.6 was not touched by the Leopard upgrade.
Could this mean that there is no Java 6 in Leopard? I'll do a clean Leopard install on a new disk soon, did anybody try that already?