This web site allows you to plug in the specs for the camera/lens/aperture used for a shot and it returns information about the depth of field you should expect, including the following:
Near limit of acceptable sharpness
Far limit of acceptable sharpness
Total depth of field
Depth of field in front of subject
Depth of field behind subject
Hyperfocal distance
Circle of confusion for selected format
Ben,
Please check out: http://www.liquidsculpture.com/dof.htm for an awesome DOF tool that allows one to easily visualize what is going on!
Paul