I think my Xtracycle, seen above on the commute from work last year, is probably the nearest to a perfect bike, and I certainly hope it will last as long as I do: the long tail allows for transporting children, books, shopping, bicycle frames, large bags of compost and probably a fair bit more besides, and gives a lot of flexibility to be spontaneous about it too.
On the other hand it isn't as heavy as our steel and plywood Bakfiets and has a mountain bike gears and feels a lot like a normal bike when riding so it can be used for touring an longer distances if I am in the mood, and the central seat is very nice and comfortable compared to the usual position over the back wheel.
The only real issues are that the long cable routing to the rear mech and brakes which make gear changes suggestions unless I keep it fairly well maintained, and the cable gets gummed up with ice in winter. Also I have to buy two chans for every change and tandem cables for the back, and it can be a bit awkward on trains, which is why I now have a commuter bike to fill in those particular gaps.
I've noticed that being car free often means having several bikes to cover all the things you would normally expect from a car...
