Wirelessly posted (iPhone: Mozilla/5.0 (iPhone; U; CPU iPhone OS 2_1 like Mac OS X; en-us) AppleWebKit/525.18.1 (KHTML, like Gecko) Version/3.1.1 Mobile/5F136 Safari/525.20)
Contrary to what was previously posted, I do think that it is normal. I have owned 2 iPhones, a first gen and the new 3g, and they both did this. Also every iPhone that I've had my hands on has done this. I think that it is just the way that the screen powers down.