I knew someone who was a nephew of Paul Winchell, the ventriloquist.
I was in the same high school class as a son of Ray Rayner, a Chicago TV celebrity. But somehow I had no idea that they were related, and I only found out about it years after graduation.
Bill Murray was also in that high school class. In fact, we were both in the glee club. But we weren’t buddies. I knew who he was, and probably vice versa, but that’s it. And I didn’t see any hint of his future comedic stardom.
My wife is related to Ethan Allen.
My best friend is the first cousin of Bill Self, Univ of Kansas Men’s Basketball Coach.
Harry Blackstone Jr. the magician lived about a block from us when I was in high school. I went to school with his son.
Christa McAuliffe’s brother worked in my father’s office back in the early 1980s.
I still fail to find the humor in shuttle accident jokes.
Oh, and I am directly descended from the sister of Ben Dowell, the first mayor of El Paso, Texas (1873-1875).
I had a good friend growing up who’s the nephew of Thurston Moore, from Sonic Youth. My friend moved to Connecticut as a teenager, where he and his family all basically live off of Thurston’s money.
I seriously dated Charles Babbage’s great-grandson during college. Other than that, I understand that my twin sister’s husband is some relation to Burl Ives, who was apparently always kind of cold to their side of the family…
Patrick Dempsey from Grey’s Anatomy grew up here and attended the school at which I now teach. He was before my time, but many of the old-timers remember him. I don’t know him, but I know his sister. I don’t watch Grey’s (is it still on?), but I hear he’s a hottie.
My father-in-law was a struggling lawyer in NYC in the late '50s/early '60s, and often traded legal services for art from (among others) Robert Rauschenberg. Yes, he still has the pieces.
My mother knows Stephen King. I’ve been in his house (before it was his–partied hard there during high school).
A friend of mine in college was from Bowie, Maryland, and at the height of N’Sync’s fame was attending high school with the younger brother of J.C. Chasez. I don’t think she knew the brother especially well, but she said he mostly seemed embarrassed about the whole “related to the guy from N’Sync” thing and would have preferred if people didn’t mention it. (I’d have felt the same way if I were related to a member of N’Sync.)
A friend of my mother’s was the TA in a college class that had Henry “The Fonz” Winkler’s daughter as a student. She said young Ms. Winkler was pretty obnoxious and very clearly thought she was entitled to special treatment.
Anyone besides me never heard of even half of these ‘celebrities’?
My children, I am led to believe by ex-in-laws, are a part of the Alden Family… This lineage includes the Adams’ family (John, Abigail, and John Q, etc.).
A bit tenuous on the celebrity relationship but there ya have it…
If we are going with ancestry, my daughter via my wife is related to both James K. Polk and Lew Wallace Governor of NM and author of Ben Hur. Her Grandfather is famous southern architect George Wallace who designed a lot of the buildings in downtown Nashville such as the Baptist Vatican. 
I went to high school with Carol and Darryl DeBarge. Went to college with Keegan Michael Key(MadTV).
My step-daughter’s cousin is Christopher Cross.
A girl I went to high school with was Kurt Cobain’s cousin. She knew him quite well growing up, before Nirvana.
This remindss me, I went to high school with Traci Lords and her sister dated my best friend.
oh, yes, and my ancestor on my mom’s side is Aaron Burr.
I knew Senator (D-MT) Jon Tester’s son Shon when Shon was in college- we both attended UM in the theatre department and belonged to a student organization together. He probably doesn’t know who I am (I was a lowly freshman when he was about to graduate, and we never worked together on anything) but I did know him.
I’m about 80% sure that I’ve met at least one of Dirk Benedict’s relatives (original last name: Niewoehner), and if not, I know two women who used to babysit him. Ah, small town Montana.
There are at least two other Alden cousins on the board here; iampunha (if he’s still around) and yours truly.
My Family is related to President Taft.
I got drunk with Jerry Pournelle at least once. It’s hazy.
My Dad and Grandfather were close friends of Senator Henry M “Scoop” Jackson, enough so I was put on his CA Delegate list (I never got to go:( )
Butch Patrick, aka Eddie Munster went to school with me.