Is the APS-C DOF penalty all that important?

rpenmanparker wrote:

I have been discussing with folks on dpreview and dyxum forums various topics regarding availability of different lens types as well as the issue of DOF penalty in the APS-C format vs. FF.

It seems to me this calls into question the DOF penalty as a reason for dissatisfaction with APS-C and as a driver for upgrading to FF. Sure there may be other reasons such as IQ for wanting FF, but I can’t see how DOF is all that important. Are there other shooting situations where the DOF difference is more meaningful?