I see ones like this in use all over China. There is a pretty steep hill in form of my school but they seem to make it up to the top. That is with only 350W, so I expect that the 600W, or 1KW units would do just fine. The only trouble is that (and this is a China spicific problem) they are beginning to face the same restrictions as bicycles; such as restriction to bicycle facilities and prohibition where bicycles are prohibited. I am also seeing them being required to be walked in places that bicycleists are required to walk (such as facility gates) where previously that were permitted to ride through like motor traffic.
It is interesting that Beijing is being forced to remove bicycle restrictions. They seem to be discovering that trying to eliminate bicycles in favor of private cars was not a brilliant plan.
http://www.werelectrified.com/electric_pedal_bike.html
I do realize that this is more of an electric moped than an electric bicycle; and as such, is not really the item under consideration. I go find it interesting that it has a much smaller motor than the ebikes that we are discussing.