WHy, yes I do. And it's interesting.
I won't disclose her real name, but she is on here(I coaxed her into joining ZD, as well as a lot of other things), bu the username battle_grl. She's been my best friend for years, even though at first sight we're polar opposites. In truth, we're as different as we are alike--she's referred to our friendship as that of "a five-year-old and a twenty-five-year-old". I really am the straight man to her eccentric, compulsive and slightly immature behavior. But we have so much in common--vivid imaginations, a love of art and drawing, roleplaying on a nearly by-the-second basis, Zelda among various other fandoms, we even listen to the same genres of music. I know so few people who listen to my genres, but there she is. I've known her for years, and she's one of few people I will easily open up to socially in real life.
Yes, she is my best friend. I think we mutually trust each other more than anyone else, family included. I feel so honored to have a best friend, an introverted person like me only stumbles on something like what we have very rarely. In that respect as well as many others I am a very, very lucky person.