"OH, MY GOD, MOM AND DAD ARE 9TH COUSINS!"

"Oh, my God, Mom and Dad are 9th cousins!"  
That's what I yelled out while doing research on a MUDD line on my mother's side the other day.  Two names that came up sounded familiar to me:  WILLIAM BOARMAN (1630-1709) and his wife SARAH SINGLEY (LINLE) (1627-1668).  Sure enough, I checked and saw that they were already in my tree, 9th great-grandparents on my father's side.  It turns out William and Sarah are also 9th great-grandparents on my mother's side.  Double great-grandparents one could call them.
Apparently William and Sarah had two daughters, one of which, SARAH, married THOMAS MUDD and went on to produce descendants on my mom's side.  Their other daughter, MARY ANN, married ROBERT GREEN and had offspring which eventually led to the birth of my dad.
I just started doing genealogy about three months ago.  Has anyone else discovered that their parents were distant cousins?  Is this common?  I'd love to hear from you.
Also would love to hear from anyone who has WILLIAM BOARMAN and/or SARAH SINGLEY (LINLE) as ancestors.