I think it is fair to say that we have all used Wikipedia as whenever you look up something on Google, it most likely is the first result. Despite its popularity the site since its inception Wikipedia has been hated by teachers and academics even though students still use it to their dismay. The common reason why there is a stigma hanging over the encyclopedia is the fact anyone can edit leading to the thought that it is the wild west of sources, despite the fact it is as accurate as Encyclopædia Britannica. No matter what your view in the matter is, Wikipedia is here to stay, so embrace it in medical education.
Full disclosure: I am a Wikipedian and proud as you would have likely concluded by the end of this. Being such a big fan and contributor of the site I attended Wikimania 2012 where a lot of us all came together to discuss how we were doing and what we should be doing going forward. One talk was given by Sue Gardener, executive director of the Wikimedia Foundation which oversees Wikipedia and various other wikis. There she revealed that all the Wikimedia Foundation web properties have a total of ~500 million unique readers monthy, and even more shocking, 2.7 billion page views monthly from the United States alone. That is quite a lot of people who use Wikipedia as a source of information, making it an Alexa top 10 website as of August 2012.