I can't quite remember the old joke I used to know about a bicycle without a seat, but here's a real bicycle design without a seat, by designer Julia Meyer. It's the Taurus, "a playful sports device for children," kind of like Nerf Crotchbats. From the Yanko Design website:
"That cushy padded seat on your bike is a fitness hinderance, preventing the toned legs Lance Armstrong would envy, and keeping your back unnaturally aligned. The TAURUS bike eschews the seat for a unique cab forward design."
I'd just like to point out that all those dudes in the Tour seem to have found a way past the fitness hindrance of those cushy padded seats.