the key saving energy, lightweight. saving rotating weight is like saving twice the weight...so lighter shoes and pedals will help. but the most important thing is fit. because cleats lock your feet into the pedals, they better fit right. I need to use cleat shims...http://www.bikefit.com/products.php

as others had said, stiff is important, most shoes go with carbon to get stiff and lightweight together.

the other thing is lightweight wheels. entry wheels come in around 2000grams. a mavic ksyrium sl is about 1550, pretty much bulletproof. but the pros go with carbon tubulars in the 1200 and under range. if you don't thing lightweight helps, try running in heavy shoes, then try it with light shoes...