I've never personally known someone named
Buffy. But there is a person on one of the Animal Cops shows(Miami, I think), who goes by
Buffy, even though her name is
Deirdre.
My Grandma also had a cat named
Buffy who was evil and the only cat ever really in the family.
Personally, I would never use the name
Buffy, as it will always be associated with the evil cat and the tv show for me.