considering that Wiki is a public updated tool - any information found on Wikipedia should be taken with a grain of salt as it's more prone to someone's opinions than actual fact . . . granted Wiki keeps up on posts and relies heavily on people tagging inappropriate or innacurate material, it's still possible to end up with bad info . . .
. . . not saying that there isn't good information there at all, I mean, it's a quick site to check if you've got a good idea about something, but just want a little info to doublecheck your thoughts.
Again, I was taught back in high school, when researching for reports and essays and the like, that something known as common or agreed upon fact doesn't really need as many sources of references - but if your topic is controversial, you want to make sure that your references have good references too (I had quite a few teachers that would randomly spot check students papers), and anything amiss can discredit your paper and hurt your final score.