No one rule is a good way to sharpen as its a pretty powerful tool.
Canon 10D's require more hsharpening as they produce softer images but conversly these images allow far more sharpening.
I use Focalblade a plugin which allows you to shepen edges and surfaces seperately and is well worth the price and then some.
I apply 400,0.1,0 to edges and 100,0.1,0.
The advantage of the Canon here is it allows between 3-5 passes with those setiings and very little noise but you could not do that with normal USM
because it hits the entire picture not just the edges.
The extra flexibility allows you to get crisp edges yet avoid noise buildup in open surface area's.
Probebly the best tool i have ever seen for PS