tekgoblin sends news of the latest iPhone 4 glitch being reported in user forums and elsewhere: the phone's proximity sensor seems not to be detecting nearby faces, as it is designed to do, in order to deactivate the screen during a call. The result is often unintended input.
"On the iPhone 3GS, the proximity sensor was located to the left of the earpiece speaker. But that space on iPhone 4 is now occupied by the front-facing camera, and the proximity sensor is above the earpiece. What's not clear is whether the iPhone 4 screen's misbehavior is due to the new location of the sensor, or it's because Apple tweaked the sensor's responses in [some] way."