Sorry, i currently have no Idea about how many files are on the net.

At http://www.limewire.com/english/content/netsize.shtml you can check the results of a Gnutella-Crawler reporting currently about 2,000,000 Users online at the same time.
The userbase of Gnutella increases every day.

So, have fun and welcome to the Gnutella-Network :-)