I have been living for seven years without a car, which worked out pretty well. Still, there are time when you want to transport bulky items, there is only so much stuff you can put into the saddle-bags. I have been considering buying a trailer for my bike for ages and I finally bought a Yak trailer from Bob.
The Yak trailer has only a single wheel and is thus quite narrow, an important feature when you are biking a lot within the city. I had ordered it by mail and delivered at work, so that I could assemble it in the bike workshop. Assembly is pretty straightforward, you need unscrew the rotating hooking part and re-assemble it outside of the frame, build the mud guard for the wheel, and you are pretty much done. Hooking is done by the way of a special rear-wheel axle that is wider and has two knobs. The trailer hooks on those knobs.
I have not yet seriously driven the trailer, just brought it back home. The cargo capacity is pretty good, and when biking in a straight line, I did not feel much additional drag, the bike does react a bit strange when turning, you feel like driving a miniature trailer truck.
I still have to figure out how to fully use this trailer, in particular for shopping: how to park, how to lock it, but it looks pretty promising.