Anecdotal at best, but I have noticed a slow decline in % of quality posts per comment thread over the last 3 or 4 months. This problem is also much more apparent when the article is about something that is easy to comment on (non-technical discussion) and one that has large groups of cult fans and detractors that will blindly support or badmouth any newly released information (apple products are probably #1).
sorry for the OT. apple sux!1