When Mr. Sweede and I got married we did not do a honeymoon registry.
But if one of my friends or family members had a honeymoon registry I just might purchase off it!
I have many friends who don't really "need" gifts off a traditional registry (I'm 30 so most of my unmarried friends have all the furnishings, appliances, etc. already). If I didn't feel like giving cash and I knew the couple didn't need or want anything like china, bedding, pots/pans, etc. I'd love to give them a fancy dinner or a couples massage on their honeymoon. The memories may last longer than most gifts off a registry will! I don't think I could buy part of their airfare or hotel stay, but dinner, swimming with dolphins, etc. I'd do.
And to the poster that said that people spend time bonding with their spouses and not doing activities on their honeymoons, I'd bet that if we took a poll most people did "something" other than eat, sleep and make lurv on their honeymoon! And swimming with dolphins, a hot air balloon ride, a hike in a rainforest, a romantic dinner, a couples massage happen to ALL be activities that make you bond with your signficant other - you try something new together, see each other reactions and have memories that last a lifetime.
You don't just bond in bed you know