You wont get notified by Google if you are hit by a Penguin (the beak marks in your shins will tell you instead). Have a look at your link profile, use Opensite Explorer but also check your Google webmasters account. Look at the link profile, not just the variation in anchor text and the number of sites linking to you but also the number of pages. We've seen an account that looked perfectly natural until you see the one directory listing (designed to be from one page) that actually resulted in over 10 000 links from dynamic pages - that is unnatural!
