Updated: September 16th, 2012
According to Wikipedia, in April 2008, the number of videos on Youtube was 83.4 million (ref: http://en.wikipedia.org/wiki/YouTube#cite_note-5). However, the link in the cite note now displays “*” video results 1 – 20 of millions, without showing the real count.
Here's one way I found to get an estimated, but relatively accurate, number of videos on the popular video sharing site Youtube. The idea is simple. Get this feed: http://gdata.youtube.com/feeds/api/videos/-/* and parse out the number inside the <opensearch:totalresults> tag.
So here it is: the number of videos on Youtube is currently fluctuating between about 141 million and 144 million. The number goes up and down, which points to the fact that these are estimates.
That's a whole boatload …