Idle up? Or idle down?

some folks have done mods which require higher idle setting to get the car to run decently (like a cam, as BmorrisJ said).
also some folks mess with the idle to try to lessen the effects of idle surge. i say if you can have it idle at 650-ish (stock), then do it. i have a few cars that idle at 1K rpm or just under, but it is to help other problems.
my two cents worth.