I was hit with 'something' in March as well though it was not sitewide. I have no warnings, have never paid for links, have never submitted articles, have not set up profiles to get links etc. I have no warnings in GWT and no manual penalties listed.
To cover my bases I did file a re-inclusion request anyway(before the new system rolled out) and was told there were no manual actions. Prior to the re-inclusion request I had gone through my entire backlink profile as provided by GWT and added each low quality link to a list barring the entire domain from being credited.
If Google is omitting the worst offenders from GWT then how am I supposed to know about them?!?
If Google is not crediting low quality links anyway then why am I wasting my time?
Something in Google's system is failing, I hope they fix it soon.