Martin,
We haven't seen another on the road since we bought one!
Mind you, the DVLA's figures suggest approx 220 in the UK and Peter Perkins (see his very useful
Buyers Guide) believes there are only 100 UK spec cars! These say "HONDA" on the left side of the glass rear panel rather than "HYBRID" for reasons that escape me, and are manuals, have headlamp adjustment, rear fog light and a cubby hole with flap under the radio/cassette).
The Kammheck ('Kamm') tail is one of the reasons why the I1 achieves such a good CDA. The rear of the car is of course more important aerodynamically than the front - keeping the airflow over the car smooth, and then allowing it to reflow behind the car with minimum turbulence is critical - hence the narrow rear track and rising undertray, like the Citroen SM.
Wheel covers are free MPG, but I guess manufacturers want to show off those big and flash (i.e. aerodynamically messy and high rolling resistance) alloys that justify a nice price uplift!