Google already knows if a page is part of a discussion group and it also extracts useful information like the number of posts or the date of the most recent post.
Now Google started to cluster forum threads and to show related discussions below some results. Google uses a similar technology for Google News, where news articles from more than 25,000 sources are categorized based on their similarity.
For now, this is just an experiment, so only a small percentage of Google's users will see the enhanced results.
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