Ok, so I'm going through lots of "buy viagra" sites just to look at what they're doing with SEO (most/all of these sites show blackhat crap). I was surprised to see that this site: no cleveland walmart.org/ (get rid of spaces) ranks on the 2nd page for "buy viagra" for Google (Canada). I've looked at all its backlinks, and it appears to be from splogs except that almost all the anchor text is "no cleveland walmart". You can check it via this tool: http://www.webconfs.com/anchor-text-analysis.php I only saw once instance of their anchor text which contains the phrase "buy viagra". Almost every other link is for "no cleveland walmart". And it doesn't look like these sites are being cloaked to deliver "buy viagra" or other key phrases to google.
The content on 'no cleveland walmart.org' also affects SERPS. If you were able to get some ridiculous amount of backlinks, say 100k or something but had no anchor text or anchor text unrelated to whatever is on your page, you could still rank for that term. Its a combination of anchor text, backlinks (quality and quantity), and on page content (keyword density).