What are the largest, most helpful forums for prostate cancer patients or survivors?
Also what are the best websites to turn to for discussion on overcoming impotence and incontinence?

I would point you in the direction of WebMD.com. This site was started by former Attorney General C. Everett Coop and is considered to be an extremely reliable site for the public to seek information. I would not be surprised if in all of their diagnostic data and millions of users that they also have forums and moderated discussion. Not 100% positive they do but it seems very very reasonable that they will.

Hope this helps...