Take the human eye, one of the creationist’s favorite examples. Some people see dark spots on their eyes when staring at very bright light (or sometimes even the blue sky). Those spots are caused by the fact that the blood vessels serving the eye are positioned in front of the optical nerves. This is a rather annoying feature, which a competent engineer would have certainly avoided. In fact, cephalopods (ie, squids, octopuses, and the like) have their eyes (which evolved independently from the vertebrate’s) built the other way around, so they don’t have to suffer from this inconvenience. The only possible conclusions are: a) god didn’t design the thing; b) god is pretty sloppy and not worthy of all our unconditional admiration; c) god likes squids a lot better than humans.
A Case Against God (pdf)