San Francisco Victory Garden

I've been following the progress of Slow Food Nations Victory Garden with interest for a couple of reasons.  First, the notion of tearing up the lawn in front of any city hall and filling it with an urban garden is pretty darn cool.  Second I was interested to see that they were using a modified "keyhole garden" design for most of their beds.  Keyhole gardens are used in a number of places across Africa (perhaps in other places as well, but I'm only familiar with those in Africa) to provide backyard vegetable production but I've never heard of them being used much in the states.  

Here's an animation put together by Send a Cow, demonstrating a bit of their design:

I had never actually seen a design exactly like the one the video demonstrates, with a compost bin built into the middle.  It's an interesting idea although I would wonder if it would be a more effective distribution of the benefits to compost separately and then incorporate the finished compost into the soil.  I would also be a little worried about it going anaerobic, as it has to be difficult to turn.  It is, however, very convenient.  In answer to your next question, the cans play a similar role to the vermiculite in your potting soil, creating space for water and air flow within an essentially closed container, although you'll want to punch some holes in them to make sure they don't trap water that turns stagnant.

The third reason I'm following the garden's progress is that I'm very interested to see how the garden is managed, maintained and used over the coming years.