I've lost a ton of things at WDW, and only one was never found. I lost a pair of sunglasses inside the Drew Carey show (that's what I get for going to see what I knew was a crappy show!) and as soon as we exited, I realized they were gone. They even let me back into the theater to check my seat as they were cleaning between shows, but they were gone. Someone must have picked them up on their way out. I never thought to check with Lost & Found later, I just bought new ones at the handy gift shop right outside the exit.
I lost sunglasses on Expedition Everest, and once again realized as soon as I exited the ride. I had put them in the little pouch on the seat back and forgot to retrieve them. Inside the gift shop there is a window where they said they sweep the ride after every two or three times, so I described the glasses and came back about 20 minutes later and they had them waiting for me!
I lost my digital camera inside Innoventions, I had put it in my pocket and it must have fallen out. I was halfway across the large open area behind Spaceship Earth, headed towards the other side of Innoventions when I reached for my camera and it was gone. I burst into tears and RAN back to the last place I remembered taking a picture (and I do
not run, lol!) and it was gone. I was frantically looking everywhere and a nice older CM asked me if I had lost a camera. I described it and he disappeared into the back and came back with it! He had seen it on the ground and picked it up, and was looking for its owner.
My DD, then almost 2, lost her hat on the Snow White ride. The CM asked us to come back in a few minutes, and they had found it. She also lost her favorite, must-have blankie with binky attached ("Binky Blankie") somewhere in FantasyLand. We ran to all the rides and asked everyone to look for it, she was so upset but hopeful because of how her hat had been found. We were frantic because it was very late, just a few minutes before closing time, and DD will NOT sleep without her Binky Blankie. Finally we asked the Dumbo CM if he had seen it, and he said he hadn't but we were welcome to walk around the ride and check. We remembered we had ridden in a yellow elephant, and sure enough there was Binky Blankie sitting in the footwell of the yellow Dumbo. He even let us ride one more time, the last ride of the night and it was just us on the whole ride.
We've lost a few pins here & there, but we've also received a few free pins so it evens out.
DD's grandpa left his camcorder inside the big "tent" store in Toontown and went back about 20 minutes later, and they had it there. DD was buying the My Little Pony box of pick-your-own stuff at the time (again it was near closing time) and they let her fill not only the box, but the entire shopping bag the box went into! Then they took us outside and showed us a great spot to view Wishes.
Not a lost but a found: My older DD, then 8, found a wallet in a handicapped bathroom stall in MGM, the one on Sunset Boulevard. I took her to Guest Services to turn it in. We peeked inside and it had a lot of cash inside as well as credit cards and park tickets. I hope it was returned to the owner. DD was a little disappointed that the CM she turned it in to didn't "reward" her or even thank her, but she said knowing the person would get her stuff back made her feel really good, and she never once thought about keeping any of it. We also once found a ticket on the floor outside the bathroom near Crystal Palace and went out of our way to turn it in. I don't think it would have been able to be returned, since it was just a paper ticket, but I felt it was important to set an example for the kids and turn it in anyway.
I guess we've been very lucky about not losing anything valuable in WDW.