A new report from the Pew Institute (PDF) tries to pin down why Wikipedia is so popular: the sheer volume of material, sheer convenience and search engine friendliness. Actually, I’d add another reason, which is driving a growing proportion of my visits to the site: Wikipedia as pseudo-search engine. If I’m looking for the primary source for something – be it the official site for something or other, or the primary reference document – it’s invariably included among the Wikipedia page’s external links. With people wising up to SEO at differing paces, I’m occasionally having trouble finding that primary source among the first few pages of Google results. Wikipedia rarely disappoints.