Quiet bikes are good
One problem with riding in gravel pits (or in my neck of the woods - alpine forests... with gravel pits) is the noise upsets the neighbors (perhaps the ones who move in on a Monday and by Sunday have phoned the police, mayor, newspaper, bureau of land management, etc.).
Not pissing these people off is, for the thinking off-roader, an absolute dream. Some of us already go to such freakish lengths as leaving our stock mufflers on (and other travesties) to try and help. We such are outnumbered five to one by people who don't care if they can't ever come back, as long as it sounds (and feels) like they're riding a repeating cannon.
These people remind me to fondly look forward to the government, for the common good, restricting some riding areas to electrics.
On the road, someone wisely mentioned "... electric bike[s] might be too quiet for the average pavement crawler to notice them coming". It has been my experience here that half the pedstrians can't hear anything short of a furniture truck over their iPods and the other half don't care what they hear - they'll look at you and walk into the street anyway.
OK, some people use their ears instead of looking. Bicyclists and Priuses are already struggling with this, and when the wind is right or there's a sharp curve even regular engines can't always be heard coming.
I'm all for going electric and on the listening end being able to get more sleep / relaxation and on the riding end not having to change the oil, worry about melting my bag, fight to get it to start at midnight in Winter, etc.. And I'll continue to look both ways before crossing the street.