I have written about endogamy before:
DNA ~ Chromosome Browser and Endogamy
One Jewish Family's DNA Ethnicity Results (at FamilyTreeDNA)
and I usually mention it in my blog posts about DNA.
Due to endogamy, my husband's match list at FamilyTreeDNA has 9,902 matches. Yes, that's a lot. (I have 2,403 matches, and some of them appear as closer relatives than they really are due to endogamy, because of my many colonial New England ancestors.)
Recently I noticed a fellow blogger's name in the match list for my husband's DNA test results, at both FamilyTreeDNA and at GEDmatch. She shares more DNA with my husband than she does with either of his parents! This match is Emily Garber of (going) the Extra Yad, a blog to check out if you have Jewish ancestry.