Hey, it's me, old-stick-in-the-mud, wrt upgrading Java For the most part, I think the same arguments as last time (Java 1.4 -> Java 5) still apply.
However, Oracle is so much more aggressive in obsoleting their software. They haven't patched Java 5 in quite some time. When Lucene went to Java 5, Java 1.4 was still being patched.
I think most will be running Lucene under Java 6 (excepting some versions of Mac OS X and hardware. E.g. Core Duo Macs can't run Java 6).
I'd like to see that we have api compatibility w/ Java 5 (i.e. it can compile against Java 5), but certify against Java 6. This would allow it to run under Java 5, with the appropriate caveats that it is not supported or tested.
If you do go to Java 6 features, then I think it has to be a 4.0 release and the planned 4.0 might need to be bumped to a 5.0 designation.