I like the reverse trike layout, but I can't get excited about tandem seating. Anyone who's ever sat second on a motorcycle knows what I mean...
A side-by-side version would weigh very little more and provide full fun for two. maybe something like what VW or Peugeot did, but using the DIY approach exemplified in the article.

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Best tank ever: 72.1 mpg in February 2005, Seattle to S.F.
New personnal best 'all-city' tank June '08 ... 61.9 mpg!
Thanks to 'pulse-n-glide' technique.