Hi Cas:
I've read that you use JET to produce Win32 executables with decent (great?) success, but you are looking to move away from JET. May I ask why?
I think you alluded to cross-platform issues (but then again, if you already have a licensed JET, wouldn't it make sense to use what you can for the platforms at hand?), but just wanted to confirm.
Secondly, has anyone looked into the completely of GCJ as of yet and for its suitability for producing cross-platform native binaries? I looked through their website and noticed there's work yet to be done, but is it complete enough (or will it be complete enough?) to work for LWJGL and basic games development? For instance, AWT is not completed yet, but LWJGL doesn't use AWT. I wonder if the bare minimum is working... I know the windows version is a bit lagging, as well, but if you have JET, then you could build with JET for Win32 and maybe look into GCJ for linux and other platforms..
http://gcc.gnu.org/java/status.html is a reference page for you to look through if you haven't already.
Maybe I'm clueless, though.