Roberta Estes is a very competent genealogist with extensive credentials in the field. If you're familiar with her blog "DNAeXplained - Genetic Genealogy"you'll likely agree. If you're not familiar but have interest in DNA and DNA research, I suggest you go to her blog and subscribe.
Rather than have me attempt to describe the goings-on at 23andMe, I thought it would be best to simply offer the link to that specific blog to read at your leisure. All you have to do is click here.
She'll do a much better job that I could ever accomplish!