We all are aware of the Google duplicate content penalty and take due care that this does not happen with our site content.
But, what to do when you have a site where users are themselves authors: they post in your forums and blog on your site as well. The users might be posting scrapped content on your multi-user blog or forum.
Will this too attract Google penalty as the site owners have limited control on what users are generating as content.
Keeping a check on which UGC is duplicate would be an enormous task.
AFAIK the "penalty" applies to the duplicate content, not to the site as a whole. If you have a site with 90% original content, and 10% duplicate content, the original content will get Google traffic without penalty. There may be a tipping point where too much dupe content in a site affects the whole site, but it doesn't sound like you are likely to reach that point.
Does Google understand that this being UGC, discount it as duplicate and move on?
They almost certainly do. We can spot the copied articles on our site by looking at lack of referrals from Google and comparing it to other articles in the same niche.
My advice is to create an algo that dumps articles every so often which receive little or no traffic, this will effectively eliminate the problem before it turns into a penalty by keeping the ratio of copied content to unique content low
[edited by: dataguy at 2:10 pm (utc) on Oct. 28, 2009]