They've been doing this for months, and it's done revenue-sharing style, so if you're getting a lot of comments, you stand a chance of making a couple of bucks through the ads. (If you go to your admin page and click Analytics, you'll see the discovery tab which tells you how much you've made.)

I've gotten multiple emails on it, so it certainly wasn't a bait and switch. A piece from November on the matter:

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The new Promoted Discovery for Disqus was a major release for publishers like you who are seeking ways to drive business around content, community and conversation. We’re very excited about the results so far. There’s strong engagement in discovered content and excellent flow of new high quality traffic for websites using Disqus. This tells us it’s winning for both publishers and their readers.

We’re only getting started. As we grow, we'll continue to evaluate new opportunities for you to grow and make money with us. We think you’ll like them because, like Promoted Discovery, they will be complementary to the user experience. If you’d rather not try out these features, you can always turn them off in your settings.

The next feature we’re piloting lets you get credit for the traffic you drive to ecommerce sites like Amazon or eBay. If you already do some form of affiliate linking, we do nothing to those existing links. Soon, you may begin to see the impact of these in your reporting dashboard (we’ll be rolling this out slowly over time). Of course, all of this happens seamlessly behind the scenes — the experience for your readers doesn’t change at all. You can learn more by reading this page.

At Disqus, our core philosophy is to remain native to the core user experience and provide the best community experience possible. As always, I welcome your questions and feedback.