I think people should definitely do this. Discussing your end of life wishes really has nothing to do with your spiritual life. That's in someone else's hands. What happens to you and your stuff, however, will be left to your relatives to figure out on the spot. If you don't want the family standing around screaming about what Mom Surely Would have Wanted, it's best to say it up front.

Do you want heroic life-saving measures? To be an organ donor? Cremation? Funeral? Burial in family plot? Your sister to have that favorite piece of cross-stitch or the family dining room table? If you don't spell it out ahead of time, you can bet that nothing you might have wanted will happen.

My relatives are crazy enough that they're hard to deal with even if wishes are known, but you at least have something to threaten them with. My sister had talked my dad into donating his body to science (a worthy cause but not something he was interested in) because she was helping herself to his money for years. That's at an end and we have discussed his cremation and eventual burial at Arlington National Cemetery. He is so relieved.