bbPress.org

1. No security problems most of the time. Every WYSIWYG editor I’ve seen allows the use of certain HTML code, and everything else is stripped away. With any piece of code, there can always be vulnerabilities, WYSIWYG or not. Without a WYSIWYG editor, there can still be cross site scripting and SQL injection errors.

WYSIWG editor vulnerabilities

http://www.google.com/search?q=WYSIWYG+editor+vulnerabilities

2. Yes, it is used in large forums.