Yesterday Matt Cutts announced https://plus.google.com/109412257237...ts/gik49G9c5LU
that webmsters may have recieved "unnatural links" warnings in the last 24 hours.
The information given seems a little confusing, because on the one hand he says "don't panic"
because it may not be your fault that spammy sites are linking to you, but on the other you may experience a drop in traffic.
Some additional analysis of these warnings can be found here:
If you have received such a recent warning, what are your thoughts and what (if anything) are you planning on doing about it?