Riding on the BART train to San Francisco, I saw a dozen people with iPhones -- a third of them had shattered screens. It's a big problem, especially with the iPhone 4 and iPhone 4S, which have glass on both the front and back. But a solution is on the Macworld | iWorld show floor, called Nitro Glass. It's a tempered glass screen protector that's hammer tested; salespeople were banging iPhones on the table with no ill effects. Cost: $40.