It might pay to think about the future of farming in your project, if you are amping up the "garden" program
http://www.smh.com.au/technology/sci-tech/future-farms-to-be-run-by-robots-20100906-14xpd.html

For those of you thinking of a small masonry unit (incl. Jim), look at this:
http://thedesigncritic.wordpress.com/2010/08/03/can-you-curve-a-brick-wall/

Jo