Having had a good sit on one now i'm not sure i'd want to spend a long time cycling one, they weigh a fair bit...somewhere around 23kg which (although great for toning flabby legs) is two and a half times the weight of the bike I ride most days- despite this, one was recently ridden the 450 miles from Newcastle back to London. There's some great blogs out there dedicated to a growing community of Boris bikers- you can join in here
London is a fantastic city for cycling and cyclists, it seems that everywhere you look there's an old moulton, a vintage tourer or a fab fixie resting casually against a railing...I'm popping back in a week or two so will try and get a few more pictures of the best.