For those of you who have a 3G, please note: Apple has received reports of the metal prongs [on the USB power adapter included with the iPhone 3G] breaking off of the adapter and remaining lodged in power outlets, creating the risk of electric shock.
http://www.apple.com/pr/library/2008/09/19alert.html
also see:
http://www.macrumors.com/2008/09/19/...power-adapter/