Does having other people's articles on your site penalize the other pages in your site? I was thinking about creating a subdomain for the library which will have lots of other peoples articles on it. Whats the best approach?
Best approach IMHO is: a] preferably only have the articles on same topic as your website is b] try to ad some other content that will make the pages unique in the eyes of search engines. But that is an extra step, probably unnecessary in many cases.
The more extra content you add to the page where you use the articles, the less like you are to fall foul of any duplicate content penalty.
Google will not penalize sub domains, directories, or files alone. Therefore, it is good to maintain clean and unique site. Do not worry about the size of your site. If you think it is too small, try to do something new, which others haven’t done yet.
Get quality backlinks to that sub domain. Have quality content and make navigation of that sub domain easily accessible and easy flowing. You should make into Google!
yes, this can have a dub penalty. You can add some related content around the article, or better yet, ask visitors to review the articles you have added.