Peter, thanks for pointing out this blog. It's terrific and one that everyone interested in genetic genealogy should read. It makes some great and very valid points. It also points out something I always tell newbies to DNA, which is the importance of having as extensive of a family tree as you can in order to be able to successfully identify the ancestors whose DNA you're sharing with others.
In the comments, Jim Bartlett had a great one: "My estimate is that the sweet spot for atDNA Matches is 6-8th cousins – that’s where the bulk of our Matches lie. Let’s take the 7th cousin level (256 GG grandparents, 8 gen back) – even with pretty good Trees, most genealogists may have 50% of their ancestors identified, or 1/2. With a Match who also has 1/2 identified, we’d only find a Common Ancestor maybe 1/4 of the time. And this is considering one of the very best outcomes. The point is that our Trees are the limiting factor, not the atDNA, IBS, miss-calls, etc. And that’s presuming this 7th cousin match will reply to your email/message (subtract another 50% or more), or even has a Tree of any merit (subtract another 75% or so). By the time you factor in all the issues, there’s slim pick’ns… So my constant harangue is: genetic genealogists need robust Trees (as many ancestors as possible; and I’m now adding children of ancestors, because so many of my matches cannot work their TN, KY, MO ancestors back to VA, etc. )"