I own an article directory (PR5), until a couple of days ago I've been approving articles without checking if the same articles have been already submitted to other article portals, then I changed my TOS and started to reject articles if they already appear on other sites exactly as have been submitted on my one. However I think it's a drastical solution as I could see my site stopping publishing fresh (even if not 100% original) content. Do you think is ethical adding a TOS term that allows me to replace some words of phrases of the article to make it unique? Also, how many different should be 2 similar articles to be considered by Google as different (=unique)? Is there some software/script that can help me with this job? Thanks for suggestions.