Description
Provide verbiage so that user comments and other user submitted content is clearly under a free/libre license (CC0, CC-BY, CC-BY-SA).
In my opinion, one of the reasons for StackOverflow's success is that the questions and answers are provided to the community under a free/libre license (CC-BY-SA 4.0). StackOverflow (SO) terms of service specifically addresses the point (under "Subscriber Content") and users who post on the site agree to provide their content under said license so that others can share and distribute it:
You agree that any and all content, including without limitation any and all text, graphics, logos, tools, photographs, images, illustrations, software or source code, audio and video, animations, and product feedback (collectively, “Content”) that you provide to the public Network (collectively, “Subscriber Content”), is perpetually and irrevocably licensed to Stack Overflow on a worldwide, royalty-free, non-exclusive basis pursuant to Creative Commons licensing terms (CC BY-SA 4.0), and you grant Stack Overflow the perpetual and irrevocable right and license to access, use, process, copy, distribute, export, display and to commercially exploit such Subscriber Content, even if such Subscriber Content has been contributed and subsequently removed by you as reasonably necessary ...
Though there are many sites that effectively duplicate SO, SO remains popular and there's probably an argument that even though there are many copycats, SO is probably enhanced by the duplication rather than inhibited by it.
Contrast this with Hacker News (HN) and their restrictive prohibition on using other people's comments on their site:
Commercial Use: Unless otherwise expressly authorized herein or in the Site, you agree not to display, distribute, license, perform, publish, reproduce, duplicate, copy, create derivative works from, modify, sell, resell, exploit, transfer or upload for any commercial purposes, any portion of the Site, use of the Site, or access to the Site. The buying, exchanging, selling and/or promotion (commercial or otherwise) of upvotes, comments, submissions, accounts (or any aspect of your account or any other account), karma, and/or content is strictly prohibited, constitutes a material breach of these Terms of Use, and could result in legal liability.
There's a saying by Quinn Norton that says
All data, over time, approaches deleted, or public.
I'm a fan of the HN community but the restriction on their user provided content is a mistake, in my opinion, and I worry it's inevitable that the HN data is lost or unusable in some pretty meaningful ways. If HN ever did decide to give the data to the community, my bet is that it would be at a point when they're shuttering and "throwing it over the fence" at which time it's utility would be a shadow of what it is now.
It would be nice if SN could avoid HN's mistake and make sure to provide user submitted content in what I believe is the spirit in which it was created, as a resource to the public and available to everyone, even for commercial re-use.