Let's take an example search: "how to treat a stye"
#1: http://www.beauty-cosmetic-guide.com/stye.htm -- There are 14 Google ads above the fold, the page is a mess, the content is crappy.
#2: http://www.howtoall.com/Healthfiles/howtotreateyesty18.htm Fewer ads, content still crappy.
#3: http://www.ehow.com/how_2107785_treat-stye-home-remedies.html eHow.com is actually a reasonably decent site.
#4: http://www.webmd.com/eye-health/tc/styes-and-chalazia-home-treatment WebMD is a reputable site, IMO.
#5: http://www.eyestyetreatment.net You can tell by the URL that it's a spam site.
#6: http://www.health-disease.org/eye-diseases/eye-stye.htm Spam site.
#7: http://www.bestincosmetics.com/popular/stye.htm Spam site.
#8: http://www.wisegeek.com/how-can-i-treat-a-stye.htm Wisegeek is a spam site that seems to show up all over the front page of search results.
#9: http://www.howtosite.net/articles/how-to-treat-a-stye.html I can't even get to the page, but it's not like I need to. I looked at the cached version, though, just for good measure.
Bottom line: seven spam sites, two real ones.
A better search, for fairness: "how to take a picture of the moon". A real site (mine, in fact!), spam, spam, real, real, real, real, spammy (but seems like it should have been legit at some point), real.
It's easy to look at these sites and see a huge sweatshop of people in India or China or Russia cranking out articles that are either cut-and-paste or slightly paraphrased from other sites, all of them designed to be highly search engine optimized. There's some simple tech on the backend to build out pages, buy domains, etc.
Yeah, I know it's a constant cat-and-mouse game-- spam sites figure out how to game Google's algorithm, Google adapts, the spammers adapt, lather rinse repeat. Still, it seems especially bad right now. I wish there was an easy way to tell Google "never show me results from this site again."