How many Linux distros are there?
The quasi-official number is somewhere around 359.
However, recent scientific research now puts the number of Linux distros at 1.5 times the number of actual Linux users.
DistroWatch database summary 08/19/2008
* Number of all distributions in the database: 572
* Number of all active distributions in the database: 349
* Number of discontinued distributions: 137
* Number of distributions on the waiting list: 201