When I was the bride/new mom, the real "gift" of wedding/shower/baby gifts was that I didn't have to shop and pick everything out. That is a huge amount of work.
I'd much rather just put a couple of big things on there, or a china pattern, or some representative colors/styles, and not have to think about it too much. Boxes full of surprises are a lot more fun than checking things off an inventory list.
When I am the invitee, I consider the registry as a guideline for relatives and family friends who don't know the happy couple very well one-on-one, or knew them better when they were younger and don't know their current taste. If it's a good friend I'm close with, then I'm going to look for a gift that will carry some memory or association of our friendship, or that I know will delight them.
When my high-school best friend got married, I gave her cunning little antique wooden jewelry box that was made to look like a miniature Chinese lacquer cabinet. It had the most twee little drawers and knobs, and I put a couple of pieces of inexpensive jewelry and crystals that represented different experiences we'd had together, and a tiny rolled-up "I love you" note in one drawer. She loved it and teared up.
That's what I call a really personal gift, and you can't register for something like that. But of course, every wedding guest isn't going to be in a position to know those real warm-fuzzy things.
We got one wedding gift that was a real doozy, from mother's best friend's daughter (who, IIRC, wasn't actually invited. She just felt obligated to send something because my parents had been very generous to her at her wedding). It was this huge painted wrought-iron contraption that was about six feet long and two feet high, that sort of looked like undulating vines with abstract floral and leaf shapes, painted in garish tropical colors. It must have weighed 200 pounds. She sent it to my parents' home, because we were married in my hometown. Unfortunately, we were going home to a tiny apartment in a faraway city. This thing was longer than our sofa.
I had to get my mom to do some delicate questioning to try to figure out what the heck it was. Turns out it was a plant stand for the patio, and the giver expected lots of gushing appreciation because apparently it was made by a popular local artist in her beach community, and cost a pretty penny.
We didn't have a patio, not even a balcony. And no way to get it home - we would have had to rent a truck and drive for two days. And it was completely hideous. But I wrote an appropriately gushing thank you note, relying on phrases like "astonishing" and "overwhelmed" and "what a surprise!"
Really, I can't imagine what the giver was thinking on that one. But we have a story for the rest of our lives. I think, all in all, we got more enjoyment out of that horror show plant stand than we would out of a set of towels or spoons off the registry.