Maybe I'm going senile but I thought filenames on the Mac were case sensitive (e.g., "test" is a different file than "TEST") just like under Linux. Working in the terminal today, however, I found to my amazement that this isn't true. I've been a Mac user since 1984 but now I'm really questioning my memory and/or sanity.

Is the Mac (Leopard OS) case insensitive or is it not?

I would more personally question your sanity. Why in the
world would anybody want case sensitivity in file names???
Is your vocabulary so limited that you can't think of words
to name your files?? Anyway, to answer your question, the
apple developers are finally coming to their senses and
decided to do away with stupid features like case
sensitivity. However, the leopard has a touted feature
called Time Machine, which is like the Windows System
Restore on crack. Never in my life have i seen a proficient
way of squandering disk space. If you're looking for a new
operating system that's fast and easy to use i'd
recommend Windows Vista Ultimate. But if you're a low
life geek and you prefer to tinker with computers on your
free time instead of being active in your community then, i
would recommend Ubuntu Linux.

Cheers!