Scott,
I agree that the real application of DEM has been disappointing (so far). However, DEM is the one unambiguous function that can be derived both from models and observations. It is therefore a unique point of comparison between them; more so that the intensities of a few lines. DEM could also in principle be defined for non-steady state ionization, although we have not yet developed the way to treat such observations. It is probably not applicable for non-thermal distributions.
Alan Gabriel
loops@solar.physics.montana.edu