Not a huge mistake (although I've made millions of those..), but I have a walhanging in our guest room and there is one, just one, half square triangle that is turned the wrong way.. Aaarrgh!!! Well, it's been hanging there for years now, and not one person has said a word about it - except my daughter, whose room it was originally, and she said she noticed it one night when she couldn't sleep and was counting the squares in the wallhanging. I have sworn her to secrecy and all's right with the world.... except I still look at that one half square triangle every time I go in that room, and just shake my head.... Well, I'm not perfect (really!) so I guess I can't expect every quilt to be perfect.