I actually meant to add this to Mike Sanford's thread. Well, here it is anyway.
I try to use the motor sparingly, because it can make one lazy. But, when I get to a hill, I use it and I'm up the hill without wobbling. It's also useful when starting up. Again, no wobble.
The range varies according to terrain, rider weight, etc. It has 4 levels of assist and 4 levels of generation. In level 1, the range is approximately 60-70 km. In level 4, it's around 20 km. I'm 160# and the terrain in NH varies from flat at the seacoast to hilly just about everywhere else.