Literally every field I have even a passing interest in has got people at the top of it who express interest in multiple fields at once. In the web-related world there's Shaun Inman, who goes back and forth between music, web design, and creating video games. Or there's Ze Frank, who goes back and forth between writing and designing tools and music and video comedy and I don't know what else. In music there are a lot of people who specialize in many, many different things at once — either different types of music (multiple instruments, or multiple performance styles, or music production) — or actively in different fields at once. Peter Brotzmann, one of the best free jazz saxophonists, is also a graphic designer who's designed all of his albums to date. Tom Waits is a musician who acts and writes on the side. Auteur directors tend to be involved in five or six different fields at once: James Cameron is a masterful set/costume designer; David Lynch handles the audio production for his movies; and writes some of the music for it. Stand-up comic Louis CK writes, stars in, directs, and edits his show Louie, which is to some degree insane.
The problem with looking at the Internet for polymaths of the same caliber of Carl Djerassi is that the Internet generation is too young right now. Ze Frank, who is in some ways the grandfather of the modern Internet creative movement, is only thirty-eight years old. The real Internet generation, of the people who literally never existed in a world where the World Wide Web didn't, was born in 1990. They're twenty years old. They're me.
I can assure you as somebody who's closer to that generation than most of the users on that site: We're going to see an explosion of creativity the likes of which we haven't seen in decades, if ever. The kids I know in high school are busy writing, drawing, making music, arguing philosophy, arguing economics, doing pretty much everything and doing it all at once. Give it thirty years and I think you'll be flabbergasted at what we produce.
When I was eighteen I'd already published a novel, directed a play, written and co-performed a song, co-created said song's music video, performed and co-wrote a Harry Potter dub, wrote multiple essays, and designed a number of web sites. A friend of mine who's a year younger was keeping a political/economic blog and engaging in discussions pretty much everywhere. Yet another friend is a hypnotist, writer, and web designer who I might be making a documentary about this coming summer. The guy I live with, twenty-one, is a talented actor who's also written for the Colbert Report, interviewed celebrities, and in his free time sells tickets. Is that polymath enough for you?