An intrepid Wikipedian named Nikola Smolenski has calculated how much paper it would take to print out the English entries in Wikipedia and produced this handy chart showing the relative sizes of the pile of paper and an adult male. This doesn't include the History or Discuss pages, which would make it a lot less useful than electronic Wikipedia (nevermind the lack of a search interface!). I think that Wikipedia is one of those documents that is inherently electronic.
Here's Nikola's assumptions: "Using volumes 25cm high and 5cm thick (some 400 leaves), each page having two columns, each columns having 80 rows, and each row having 50 characters, ≈ 6MB per volume. As English Wikipedia has 4.4GB of text (October 2006) ≈ 750 volumes. Note that this is conservative estimate, as it doesn't include images, tables etc. which take up more surface than the text which describes them."