Okay, so a Partial Matches action listed in a couple of our clients' GWT accounts says:
"Unnatural links to your site—impacts links
Google has detected a pattern of unnatural artificial, deceptive, or manipulative links pointing to pages on this site. Some links may be outside of the webmaster’s control, so for this incident we are taking targeted action on the unnatural links instead of on the site’s ranking as a whole."
Which is not a penalty on the site, but a discrediting of the links, which given how crappy some of the links are, doesn't sound much like a penalty to me. And then if you follow the 'learn more' link to further info on the links you see:
"If you don't control the links pointing to your site, no action is required on your part. From Google's perspective, the links already won't count in ranking. However, if possible, you may wish to remove any artificial links to your site and, if you're able to get the artificial links removed, submit a reconsideration request. If we determine that the links to your site are no longer in violation of our guidelines, we’ll revoke the manual action."
Which doesn't sound very logical. If we get the links removed, then the revoking of the manual action would be pointless, as the manual action was discrediting the links already, not penalising the site, so their removal would only achieve the same as the action.
Action does not equal penalty, it seems. Hmm. Watching this space...