There's a story I heard that I can't track down anymore, about a game company that kept getting strange unreproducible errors from customers. They built a RAM test into their game and discovered that most of those errors were coming from bad RAM. 1% of a lot is a lot!
Doom 3 inadvertently did this for me one time. It loads data from pak/zip files and does a checksum verification. Which is how I discovered a defective RAM stick I'd used in a new system build.
