Human-electric hybrid bikes are getting very hot in Europe with several serious manufacturers showing systems that go well beyond what has mostly been a hobbyist level retrofit to date. The notion is that people want exercise and low cost transport, but also want the option of moving without breaking into a sweat or being able to tackle the occasional hill, heavy load or longer trip.
Most of these designs are not well integrated into the bike and the finished products are often expensive - $3,000 and up is fairly common for a good quality ebike (there are many junk bikes from China and Southeast Asia these days that go for under $1,000 - I would recommend staying far from them).
SRAM, a major supplier of bike parts, is showing a two speed unit aimed at bike OEMs and possibly those who want to convert an existing bike. Basically a hub with an enclosed two-speed planetary gear transmission and a specialty rear cargo rack with a slot for the battery. The first electric assist speed helps get up to speed and up hills, the second is for cruising along at a 25 km/hr limited speed. There is no user throttle - everything is automatic, but the claim is it still "feels" like a bike. I'd have to ride one to see if it worked as promised - there are a lot of schemes for power augmentation, but this is far and away the simplest for the rider.
A bit of searching reveals a preliminary user manual and a spec sheet. Look for it in 2013... by then there wll be several competitors - even in the US. If you are serous about an ebike - any ebike - I would recommend spending time taking riders as various flavors are very different and offer differing user expeiences - what one person likes may not be what you like. Also check into the warranty, Most of these designs are very new and not exactly proven at this point. That said this can offer a very cost effective short and medium range trip alternative for those who don't want to supply all of the power themelves.