Around 11:46 UTC we reached 5 million files on Commons! Not quite sure which file is the 5th million, but this is one of the candidates:
http://commons.wikimedia.org/wiki/File:Kj%C3%B8benhavnsposten_28_nov_1838_si...
Thanks everyone for making Commons such as a fantastic project, and creating the world's largest repository of free images!
-- Hay