Maxim Integrated have a bunch of really good tutorial information on their website. This one, on PCB grounding in mixed signal designs caught my eye. Concerns over the performance of the ADC in my new micromouse, D4, have made me look again at all aspects of the design. It is too late for this version but I have plenty to learn for the next one.
http://www.maximintegrated.com/app-notes/index.mvp/id/5450