I saw this recently on a RacerMate Velotron. 62 teeth, that's right. Hugenormous. There's enough market that FSA is producing them, but besides stationairy lab cycles, who is using these? People trying to break the hour record? Racing recumbent riders with small rear wheels? Micro folding bike riders trying to avoid the clown pedal stroke?
The Velotron is a pretty cool machine that has a very adjustable bicycle-like riding platform and the ability to vary resistance and measure power output. It is linked to a computer system that is interactive in that the rider on the screen moves as fast as you move, and the hills on the screen can be reflected in resistance on the machine. Courses can be programmed into the computer so even when it's snowing out, you can mimic your upcoming time trail and all the things (except cross wind I guess) that you'll encounter. A serious tool for people serious about athletic performance.