Star Trac makes a computer that shows HR, Cadence, and yes, distance, that fits the Johnny G bikes. (Although you may have to fool with the way it attaches to the handlebars if you have an older model) You don't need to pay attention to distance if you don't want to.
My gym uses the cycle ops spinners with all the numbers, (including resistance, which the star trac can't measure, unfortunately) and I became addicted. While the "distance" is debatable, cadence is not. Without that number it is oh so easy to go 70 when you should be going 90 or 100, and to think you're sprinting at 120 instead of 140. I see it all the time in class. Yes, of course high cadence and low resistance is also a cheat, but cadence and heart rate are great numbers to have right there in front of you.