I had noticed that blogs/sites i worked with using Swedish, rarely need any other plugin than Akismet. Some of the sites has a lot of traffic. While on english and mandarin based blogs, i switched over to Disqus (actually i'm going that way with the just mentioned swedish blogs. Mostly for the simplicity) because the spam amount was overwhelming, even if Akismet in combination with other plugins did a good job.

I haven't seen a decline of comments with Disqus for the sole reason that the blog is using Disqus.

But i have seen stagnation in the number of user comments in the Swedish blogsphere (the only ones keeping up ”business as usual” is techblogs). The trend the last years is that most comments is now over at Facebook. I think this is somewhat a global trend.

You share your blog post on Facebook, and then people comment on that post at Facebook, and not the blog itself. That's why i'm trying to look for a solution to show the same Facebook comments for that post at both Facebook and the blog. This while keeping Disqus or the normal commenting system.

The problem with this is that comments could end up in two places, and the Facebook ones are not aware of the others. Of course you could use Facebook comments, but that's not always and option of numerous reasons.