Number of Users?
 

Anyone know roughly how many users use Limewire everyday?

and what ratio of content is searched for/downloaded?

http://www.limewire.com/english/content/netsize.shtml graphs the current network and is updated about once an hour.

As for graphs of content/search ratios, I haven't come across any, but perhaps this link might help http://www.bearshare.com/stats/

There have been discussions on the Gnutella Developers Forum http://groups.yahoo.com/group/the_gdf/ about how to optimize the network so searches don't drown transfers like they can do on other networks. Actually, gnutella had to give up the very popular automatic requeries to avoid that problem about a year ago.