If you run into anything that key is going to end up in a very uncomfortable place!!
shuttlebuddy.com/
I am considering at a second hand rig for CAN$300.00. With a lower profile tyre these can push a 17kg DH bike + 80kg rider along a flat paved road at 40kph. I figure it could push my 10 kg XC bike and me @ 72kg along at 50kph pretty comfortably 
shuttlebuddy has a really cool form factor... but 2 stroke engine? They're REALLY loud.
If only it had an electric motor, with the battery where the fuel tank is + a wireless remote accelerator.
The battery + motor would add a fair amount of weight the roller <> tyre contact point.
Loud like "chainsaw loud" . At least the pedestrians would hear it coming
To compliment this I could buy the Zounds air powered bicycle horn that punches out 115-120 decibles of pig squeals*. These things are "brown note" loud. They even have a military like switch system with a safety cover that you flip up prior to straffing your target with pig squeals*
*not actually pig squeals, but I would like to see some R&D that could make this happen
I agree Mr Float... Electric Bikes will be a big part of our future...
I can imagine a day, not too far away (20 years?), when Petrol is Triple the current price (related to earnings).
If you spend $50 per week on petrol for your commute... Turn that into $150 (triple)... Or the option might be, ride your electric bike for 3-5 days per week, and recharge it at your desk with your boss's electricity! Weekly fuel bill is drastically reduced.
