Really? I'll admit I'd never tried covering the flash on a digital camera with my hand, but out of curiosity, I took a flash picture with my Canon Powershot A80, with my finger obscuring (but not quite touching) the flash lens. I think I observed a bit of heat, but touched the lens immediately after the flash and noted no significant warmth. I then got out the camera manual, and found this caution:
"Be careful not to cover the flash with your fingers or clothing when shooting. The flash may be damaged and emit smoke or noise. In addition, do not touch the surface of the flash after taking several pictures in rapid succession. Either action could result in burns."
Who'd have thunk it? :icon_stup