If you have Google Webmaster Tools installed for your site (and you should if you don't) there's a chance you've recently seen a message about "unnatural links" being detected.
You, as me and my team first experience panic. You go back through time and think of all the links you've acquired, directories you submitted to and wonder if Google's cuddly little animal friends really did you in this time. (Silly Penguins and Pandas, I'm just trying to do honest SEO here!)
This isn't the first round of warnings either. A few months ago another round of warnings came through. Personally, I thought I was in the clear as I didn't see one then, but this time it got me. Then I heard that Matt Cutts was saying not to worry and an SEOMOZ article helped to quell my fears. Then I heard you have to worry about certain "types" of link messages from Google.
Finally, I found a blog by Search Engine Land that clarified things quickly with a picture. So, without repeating 1,000 words to cover their picture, here it is: SEO WARNING OR ADVISORY.
In summary, no one can really say if Google really is warning you about your links, but now is a good time to check.