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ORIGINAL: khodges

On those big cargo planes, you'd be surprised how much of the anhedral disappears once the plane is airborne, and all that weight is hanging on the wings. It isn't unusual for the wingtips to flex four to six FEET from their position with the plane on the ground to where they are in flight.

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ORIGINAL: Nathan King

As you correctly mentioned, dihedral enhances stability about the longitudinal (roll) axis. When the airplane is rolled the lower wing has a higher angle of attack (more lift) than the high wing which will cause the wings to level back out somewhat by themselves. A negative effect of dihedral is roll coupling.

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ORIGINAL: da Rock

The problem with considering the lift vector for reestablishing roll is that roll really has little to do with gravity or the wing's orientation to the earth. The lift of the wing, either side or the whole, has little to do with how level it is in relationship to the earth. That relationship has something to do with how well an unlevel wing carries the load when the wings are not level, but not much with how either side's lift will work to bring the wings back level.

http://en.wikipedia.org/wiki/Dihedral

Wikipedia says it pretty clearly. And mentions the common misconception about the lift.

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ORIGINAL: Nathan King

It's a little hard to see without a demonstration, but I'll give it a try. Imagine an airplane rolling to the left. In this configuration the right wing is producing more lift than the right since the ailerons are changing the camber of both wings differently. As you know, increasing lift always comes with a penalty in the form of increasing drag. This concept of adverse yaw is important since it is causing a right yaw (opposite the turn). This yawing increases the angle of attack on the low wing, effectively creating positive stability about the longitudinal axis. Does this make sense?

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P.S. Campgems, are you referring to the "single" lift vector splitting into a horizontal and vertical component in a bank? Yes, the vertical component of lift decreases as bank angle is increased and this explains why elevator (to increase AOA) is needed in turns. I don't see where the components of lift and the horizon comes into play when discussing dihedral. AOA is not a measurement relative to the horizon or ground, but a measurement relative to the angle between the relative wind and the chord line of the wing.