Where one does a DMin and why one does a DMin are very important in evaluating them. As has been said, a DMin is not an academic degree. In our (former) DMin program we accepted men for the purpose of giving them an opportunity to study and write about a particular aspect of pastoral ministry in detail. One of the problems in evaluating DMin projects was that they were neither fish nor fowl but a sort of hybrid. Our (late) DMin program hatched some interesting and significant work (Art Azurdia's book and Jim Garretson's book come to mind as two examples).
Nate is right. There is serious debate about the validity of all the "professional doctorates" (DMin, PsyD etc) because they don't require the sort of academic skills and rigor required by an earned, academic doctorate (e.g., a PhD). Properly someone with a DMin is not "Dr So and So." He is the Rev Mr So and So, DMin but it is not unusual to see people using the DMin like a PhD and, as been said, outside of academic circles few people observe the distinction.
This gets to motive/intent (not distinguishing them for the sake this discussion). One fears that the DMin is not just a course for self-improvement but a vehicle for self-aggrandizement, that the minister feels the need to improve his standing in his congregation. This gets to a more fundamental problem. If ministry of the Word is not regarded as inherently significant then we have a problem with the authority of the Word and a misunderstanding of the nature of the office of minister and probably confusion about the nature of the church and the means of grace.
Schools too have motives for offering DMin degrees. WSC got out of the DMin business just when others were getting in. When i announced, at a meeting academic administrators, that we were killing our program one might have thought that I had announced that we were drowning puppies! Why? It's a source of revenue. Many DMin candidates do not finish but they do pay continuation fees. They are relatively low maintenance and the demand for them seems to be inexhaustible.
Wayne's note re the ThM (or I might add, the MA (Historical Theology)) is a better alternative if one wants to gain some additional skills and expertise in a particular field. The ThM is a way for an MDiv student to spend a fourth year (hence Dallas' nomenclature) gaining polish and becoming a student of a specialized field. A few of our MDiv students are doing the same with the MA (Hist Theol) at WSC in lieu of a ThM. Writing a serious, academic thesis is a good way to gain skills and make progress and become a resource for the church.
My experience with what was regarded as a very good DMin program, however, left me dissatisfied with the DMin for reasons I sketched above.
