For the program idea I have, it requires that the software be written in one binary that is executeable by all major desktop platforms, meaning it needs an interpreted language or a language within a JVM. Either is fine with me, but the programming language has to balance power & simplicity (e.g. Python)
I know of wxPython but I have read that it's support on Mac OS X is fairly limited
Java sounds good & it looks good but it seems almost too difficult to program in
Any help?
I would suggest going the wxPython route, I know that wxWidgets (which is what wxPython is using) can be made to have great looking Mac apps (look at PgAdmin3 from postgresql).  While PgAdmin3 is not done in python, it was done with wxWidgets and looks fine on a mac.
Cross-Platform Programming Language with a decent gui toolkit?