The truth is, it would be very difficult to come up with a TRULY unique idea for a card. If you're like most of us who have been making cards for years, going to shows for years, going to classes for years, and reading card-making magazines for years, some of those ideas are just plain stuck in your memory. You canNOT erase your memory every time you sit down to make a card, just so that you won't be making a card similar to the one Chrissie Cardmaker made three years ago. Heck, she probably copied it from someone else herself.
That said, there IS a line crossed when you sit down with a photo of a card and attempt to copy it, piece by piece, then claim that you came up with the design and warn everyone they'd better not copy YOU! I've seen that happen and it's not pretty.......