I have personally done the y-DNA and mt-DNA tests and they seem useful if you are looking to find someone living to help you with your searching. I am not, being fortunate to have a family that moved a few miles away from Plymouth and then never left. The speaker was urging everyone in the Society to get tested. The benefit would be to the Society, which could then identify mass quantities of hitherto unknown humans who happen to be descendants of Mayflower pilgrims. Right now DNA tests are only used to help someone with a thoroughly documented line who gets stuck on just one ancestor. Would the GSMD be asking FamilyTree DNA to look through their records for people who match a particular genetic profile and so they can offer them membership? Would they do that person's research for him/her, just to get a new member? That doesn't seem fair to the members who worked for years, in many cases, to prove their connection. Furthermore, not everyone wants to be a Mayflower descendant or GSMD member and DNA results won't work for every line - some pilgrims invited siblings to come over on the next boat.
When I find out more, I will blog about it here.