Motorized bicycles.. cities pondering impact

Funny that motorized bikes are all the rage.
Even new ones are being pushed out by Schwinn at interbike

Remember before the motorcycle.. it was the bike with a motor strapped to it? Then it was termed the motorcycle.
I personally am not opposed to them because people are out of cars freeing up space and have less impact on the environment (if built properly). However I am not too keen on the ones that folks put loud zippy tailpipes on and claim loud pipes saves lives..
Whats your thoughts as these become more reality?

Article on Arizona motobikes:
http://www.azcentral.com/arizonarepublic/local/articles/2008/09/25/20080925bikeengines0925.html

Pictured motorized bike circa 1901.