The only negative aspect of casino searching is I can't scrutinize for small errors like DD's, missing initials, tiny die cracks, etc. It would have to be obvious like a large die break or a noticeable clip. When I search at work I can check for these things but not in a noisy casino with dim lighting! And even when I'm able to examine them closely, the doubling or other error has to be easy to spot.
Coin World newspaper regularly has columns written by error expert Jim Wexler and to date he's found over 60 different double die versions for the Minnesota quarters. Almost all of them are extra little bits of the tree design. He's also found extremely tiny doubling of Lincoln's knees and legs on the reverse of some recent pennies. I'm sorry, but when the "doubling" is that minute, it doesn't interest me.