Actually, I've encountered this problem myself -- very annoying...
What happened is that you saved the Terminal window settings while you
had a PyMOL session open, so OS X inferred that you were indicating a
desire to have PyMOL open as a default preference.
The only way I know of changing this
> I have a Mac TI powerbook running OSX. Every time I launch a new
> terminal window, pymol launches. For example, if I open 3 terminal
> windows, 3 pymol sessions also start. How do I stop this?
What? You don't want PyMOL to launch every possible opportunity?
Actually, I've encountered this