I was at a workshop on social software the other day and the speaker showed us a graphic on what Wikipedia would look like if it were bound in a series of books, like old-timey encyclopedias. Keep in mind, this is just the English version (which contains nearly 2 million articles at present); just the current Wikipedia articles (not older edits); not the discussions; and it doesn't include tables or pictures, just text. This is how big a bound copy of Wikipedia would be, as of August 2007:
While checking out this graphic, I then noticed this one, which breaks down what Wikipedia actually contains:
Source : http://commons.wikimedia.org/wiki/Image:Size_of_English_Wikipedia_broken_down.png
It's funny 'cuz it's true.