arikgub - 5:53 am on May 19, 2012 (gmt 0)
Here is a phenomena I have seen since Penguin was rolled out.
A completely irrelevant and weak by all means site manages to rank on page #1 for a very competitive "blue widgets" keyword just because it has the following piece of code on its home page containing a hidden link
<a href="http://bluewidgets.us">blue widgets</a>
The only time the "blue widgets" keyword is mentioned on the page is in the hidden anchor text. The linking site is completely unrelated to blue widgets, weak but looks legitimate and most probably was hacked to insert the link.
Even more ridiculous is that the bluewidgets.us site (the one linked to) that has thousands of links like this, ranks high at #1-#5 spots for this keyword and synonyms - all very competitive.
I've seen this in multiple different cases