More expensive rims have circumfrential grooves as the brake surfaces are machined into them.

However, in the case of a bike rim it doesn't make much difference, as the rubber adheres to it regardless.

If you want good stopping power from cantis, get some koolstop red eagle IIs: http://www.wiggle.co.uk/v2_product_detail.asp?ProdID=5300003397

Boosters can also help. I had excellent stopping power with Eagle IIs in Marin Lite cantilevers with a booster, with the same very firm modulation I like in the boosted maguras (although the maguras are a league ahead in terms of power available, and hydraulics require so much less maintenance than cable brakes, without changes in performance).