What a huge milestone. The frequent discount sales and huge television advertising budget likely pushed this number. But we continue to find AncestryDNA has drawn in people who do not understand the test process and complexity. They are simply sold on the simplicity in the advertising. The perception of easy, precise answers to ethnicity and finding unknown relatives has been an issue. Really hampering this also is the near total lack of numeric segment match analysis tools in the AncestryDNA site. Something critical to success with the process. Some have mentioned DNA testing almost appears like just another advertising avenue for the company. This because to get the real value of the test (the ability to contact matches), you need to subscribe to AncestryDNA's search service; a cost 2 to 5 times the cost of the original genetic test (for a years subscription). The fact that AncestryDNA has 10x the number of testers in their database as GEDmatch now makes it difficult to suggest any other Autosomal testing service.

We have had limited but good success with analyzing the small yDNA SNP results in the RAW data file. It is often enough to determine the single-letter Haplogroup and usually deep enough to suggest a deep SNP Pack to order with FamilyTreeDNA. With the frequent sales, ability to extract the RAW data file, and sheer size of their tester database, it gives us pause to maybe start considering AncestryDNA as the preferred Autosomal test provider. This especially with the uncertainty of 23andMe's impending website update and FamilyTreeDNA's miniscule tester database (even though greatly increased in size by allowing AncestryDNA transfers in).

UPDATE: In early 2017, Ancestry announced it passed 4 million testers.
UPDATE: In summer 2017, Ancestry announced it passed 5 million testers.