The best informed and most factual discussion of this topic is in "Bike for Life" by Roy Wallack and Bill Katovsky. Their book is THE best book about cycling as a core element of a healthy lifestyle that includes other forms of exercise and a sensible diet.

BFL summarizes the key studies in this area. And, the studies all agree that cyclists who ride twenty or thirty hours per week with poor saddles or poor riding position suffer vastly impaired blood flow in the crotch area. For many of these riders, that decreased blood flow leads to temporary numbness or temporary pain, or both. The reports of serious, permanent problems involve only a tiny percentage of cyclists.

The solution is very clear: your weight should be balanced between the "sitbones" of your pelvis, your hands, and your feet. There should never be significant weight on the "soft bits" for any significant amount of time.

The best modern saddles, such as the Specialized Body Geometry saddles, are designed to place weight on the sitbones, and not on the crotch. But, these saddles won't help unless you buy a saddle suitable for your own rear end. Most guys like those three inch wide saddles used by 150 pound pro cyclists. Wrong saddle.

And, to keep your weight on the sitbones, your pelvis needs to be upright. If the highest portion of your bars is level with the top of the saddle, and you ride with your hands near the stem, or on top of the brake levers, your back will be at about a 45% angle to a horizontal top tube. At that angle, your weight will be on your sitbones. And, if the top of the bars is level with the top of the saddle and the bars have a "shallow" distance from the high portion to the drops, the drops will be about at the same level as the top tube. Riding on drops that are level with the top tube places increased pressure on the crotch, but not to a painful degree.

What is sad is that millions of recreational cyclists, age forty, fifty, or sixty, have seen pro time trial on TV where the high portion of the bars is three or four inches lower than the top of the saddle and the rider's backs are down almost level with the top tube. That is the "right" position for a pro to use for a 30 minute or 60 minute time trial on a closed course. That is the WORST position for a recreational rider to use hour after hour on public roads, surrounded by motor vehicles. It impairs the cyclist's ability to monitor what those motor vehicles are doing, and those hours of pressure on the crotch are doing damage.

By the way, the studies also show that pedaling with your weight OFF the saddle increase blood flow back to normal (or higher than normaL0 in just a minute or so. Try to raise your rear an inch or so off the saddle anytime you are not pedaling, such as when you are coasting, cornering, braking. Try to pedal for a minute or so out of the saddle every fifteen minutes or so. A good workout, and good for the blood circulation.