I'm also amused that Zonker is the one who knows and understands the current news story about the dead girlfriend on Facebook hoax (which I haven't been following in Real Life), while Mike is the one who is shocked that she's not real, probably because in my research yesterday, I stumbled across the one where Mike accidentally tells Zonker that there's no Santa Claus.
A couple of more things about the strip--
With her mom abadoning her (and probably her dad did too, on an emotional level--hiring a maid, going bowling, same stuff, day in and day out that her mom fled), is it any wonder that J.J. wanted a career as a performance artist, where everyone would pay attention to her? And once she reached a certain point in her life, that she turned to large, you-have-to-look-at-it-or-you'll-walk-into-it sculpture?
As for Gary himself, he was (and is married to) Jane Paulie, who was a host on the Today show when they got married; he had Joanie and Rick married the same day as he and Jane. And yes, Jane was often asked on the show about how much of Doonesbury was based on their lives.
They have twin daughters, but I don't know if they were born around the same time as Jeff.