We're both right, doc.

Here's one of the benchmark studies on the matter:
http://www.bycycleinc.com/pages/lowe_4_saddles.pdf

This study shows a decreased blood flow to the penis:
http://www.nature.com/ijir/journal/v.../3900929a.html

This link reports a postulate that it could also be nerve compression, while also reporting on the blood flow study. I don't know of any studies confirming the nerve compression hypothesis:
http://www.emedicine.com/SPORTS/topic12.htm

My personal experience is that it is both numbing and painful, that is, very painful right around the numb area. However that may be, if you don't have blood flow, you got ED for sure. Several studies have shown that the collapsed blood vessels eventually stay collapsed. That's the reason that the temporary numbness turns into full-blown ED. Ed Pavelka was the first to "come out" on this problem. His solution, along with other measures, was to limit rides to no more than three hours.

Here's a link to Dr. Goldstein, the now famous urologist, and Ed Pavelka reflecting on the issue. It's an old article, so the saddle technology has changed, but not the problem:
http://mywebpages.comcast.net/billotto/biking.htm

If nothing else works, try this saddle. It works for sure. A buddy of mine rode the Cascade 1200 last year on this saddle with no problems.
http://www.bycycleinc.com/