Nope, never actually added power to the trailer. But I use it regularly - carried 100 lbs of marine batteries across town on my latest trip, last week.
FYI: Atomic Zombie has an example and video of an electric bike pusher trailer. His site seems to be down at the moment, but check
Atomic Zombie if you're interested.
EDIT: link to his
electric trailer page (link to vid at the bottom):