I just took a 32 GB SDHC card out of my Nikon D5100 and inserted it into the reader on my Windows PC. The card contained hundreds of pictures I shot with the camera this afternoon.
When I tried to move the images off of the card and onto a hard drive, Windows wouldn't allow me. It would allow me to copy them off the card, but not move them off. When I tried a different approach, Windows explicitly told me that I could not do what I wanted to because the card was write-protected.
So I pulled the card out of the reader -- and sure enough, the write-protect tab was set to the "Lock" position. When I slid the tab back, Windows moved the pictures off the card just fine.
Which begs the question: If this card was write-protected, how did the camera save several hundred pictures to it?