I just found myself needing scheme macros for the first time a couple of days ago. I rather like http://www.cs.utah.edu/classes/cs6520-mflatt/s04/macro-tutorial.pdf
It's obviously meant to be used as a set of slides for a presentation, but the examples given are clear and concise, and they helped me learn the syntax-rules system.
I must say though, I'm surprised that there's so little documentation on such a major feature of the language. R5RS is pretty much incomprehensible on the subject, and too many discussions on the subject seem to assume that the reader already understands the basic operation of syntax-rules.EDIT
: I wrote a guide myself: http://blog.willdonnelly.net/2008/09/04/a-scheme-syntax-rules-primer/