There are some that would say yes,
http://www.youtube.com/watch?v=n0eZynCSNyU
trails005zq8.jpg
But I for one am not there with the concept. For one thing you had better make sure that land use regulations allow it. The bikes pictured would not meet legal criteria for street use either as the engines are too many cc's.
I guess I always considered bicycles to be powered vehicles to begin with? Putting a small engine of any sort, gas or electric, does change the vibe for sure. You just have to come to grips with what your needs are and for me hauling heavy loads that would normally have to go via auto by bike is a priority. The use of motor assist makes that mission safer and more pleasurable.