Google has issued a large number of unnatural links penalties over the weekend, specifically around outbound links. The warning read "Unnatural outbound links from domaingoes here violate Google Webmaster Guidelines."
Here is a picture of one of the notices a webmaster posted:
This notice means that your web site is linking outwards to other web sites in a way that Google finds to be against their guidelines. The specific Google help article on this says:
If you see this message on the Manual Actions page, it means that Google has detected a pattern of unnatural artificial, deceptive, or manipulative outbound links. Buying links or participating in link schemes in order to manipulate PageRank is a violation of Google's Webmaster Guidelines.
As a result, Google has applied a manual spam action to the affected portions of your site. Actions that affect your whole site are listed under Site-wide matches. Actions that affect only part of your site and/or some incoming links to your site are listed under Partial matches.
Here is a quote from one of the manual actions received over the weekend:
Google has detected a pattern of links from your site to other sites that is either unnatural or irrelevant. This pattern attempts to artificial boost other sites' ranking in Google Search results. Such unnatural ranking would cause search results to show preferences for results not relevant to the user's actual query. It also violates Google Webmaster Guidelines. Therefore, we are discounting the trust in links on your site. This manual spam action has been applied to domain.com. To fix this, remove the unnatural links on your site and file a reconsideration request. After we determine that you have complied with our guidelines, we will remove this manual action.
The sites may not have seen ranking drops but Google is not trusting these sites for passing any PageRank or value to other sites until the manual action is lifted.
Forum discussion at the several threads above at Google Webmaster Help.