Still works fine on my 3GS with iOS4.
I've been having the same problem with my 3G. If I attach the iphone to the ipad adapter, it seems to recognize that the charger is connected, but the charge indicator never budges, no matter how long I let it charge. If I switch to the iphone charger, or use a USB port on my computer, it tops up just fine... weird.
I am having the same problem in that both of my iPad chargers do not seem charge either my UK or French 3G iPhones. Both iPhones are on the very buggy and slow iOS4. Resetting does seem to have solved the issue for me as well.
Wilson