I was able to attend the DM seminar given by Dr. Joan Coates 10/10/10 in Seattle, hosted by the Cascade Pembroke Welsh Corgi Club.  Dr. Coates, if I understand correctly, was not paid by CPWCC and flew in from Missouri and gave this presentation on her own time.
Much of the information she covered can be found in the DM discussions on MyCorgi and elsewhere, but here are  some of my notes:

The Coates lab continues their research.  They are now looking for "modifier" genes which may determine why some A/A dogs develop DM and most do not.

They need CONTROL SAMPLES FROM OLDER, UNAFFECTED DOGS.  If you have an PWC 12 years or older showing no signs of DM, your dog's DNA can benefit this research.  This requires a blood sample (a cheek swab doesn't give enough DNA for this purpose), thus a vet visit, but this is a big way you could help.  You can't do research without healthy controls.  Please, I hope some MyCorgi people will come forward and help this way, it would be a significant contribution. 
Remember, your UNAFFECTED dog may very well be A/A AT-RISK.  They'll be looking for "modifier" genes your dog has that may be preventing it from developing the disease.  This information might help design breeding programs to reduce the incidence of DM by including these protective genes.
 
Also, they continue to collect postmortem spinal cord and muscle tissue from both affected and unaffected dogs euthanized for other reasons.  This is a much more complicated, time-sensitive process involving a $200 kit (provided) and a vet willing to donate the considerable time required to dissect out the spinal cord (funding to pay for this is scarce, as usual). 

Contact: Ms. Liz Hansen HansenL@missouri.edu or CoatesJ@missouri.edu.
http://www.caninegeneticdiseases.net/

Notes: 
I think the terms "at risk" and "affected" are often confused:
G/G genotype is "clear".
A/G gentoype is "carrier".
A/A genotype is "at risk" -- would not be called "affected" until actual symptoms appear (often, they never do).
In Pembrokes,
G/G clear       6%
A/G carrier  29%
A/A at-risk  64%

The A allele is an ancient, widespread mutation, 79% in Pembrokes and occurs in many other breeds (interestingly, it is 52% in mixed-breeds).  Because it's so prevalent, decreasing the incidence of DM in Pems is not simply a matter of breeding only clears.  This could introduce a new genetic bottleneck, create new problems, and damage the breed.  It's important to "breed the whole dog, not a single trait".  This disease is a Mendelian recessive (with incomplete penetrance), so it's important to know how those Punnett squares work.

This is the same gene that causes ALS in humans: SOD1, superoxide dismutase, a free-radical detoxifier, but DM is apparently not a result of loss of this protective anti-oxidant activity (ALS researchers have made "knockout" mice with the SOD1 gene removed, and they don't get ALS).  Rather than a "loss of function", it's a "toxic gain-of-function"; the change of one amino acid alters the structure/solubility of the SOD1 protein, and insoluble aggregates of this junk accumulate in the nerve cells, bunging-up the system and presumably causing eventual cell death.   The same sort of thing happens in other neurologic diseases.

A/G "carrier" dogs sometimes show pre-clinical signs of this pathology.  Microscope sections of their spinal cords stained with antibodies to the SOD1 protein do show some of the protein aggregates seen in affected animals.  The age-of-onset for carrier dogs may simply be longer than their lifespan.  The mean age-of-onset in PWC is about 11 years.

There may be other, much rarer mutations (not detected by the current test) that could cause the same disease.  This is the case in human neurology as well.
It is apparently not an autoimmune disorder.
"There are no treatments that have been clearly shown to stop or slow the progression of DM".

Dr. Coates showed video of affected dogs in various stages of the disease.  I'd never seen this.  It was unexpectedly moving.

If you have an affected friend, check out http://pets.groups.yahoo.com/group/wheelcorgis/
There are over 400 members!

Hope this helps and I've got it mostly right.