Websites that closed down their comment sections:

• good overview: moderated [1]
• [2015] DailyDot, The Verge
• [2014] Reuters, Re/code, CNN, Chicago Sun-Times
• [2013] Popular Science

Websites that made user comments more difficult to see:

• [2014] LATimes

Websites that don't show a comment until it's been reviewed first:

• New York Times
• all Gawker sites (eg. Jezebel, Gizmodo)
• Amazon