The author, Alexander Wolfe, says DistroWatch.com currently lists 359 different Linux distributions:
True, some distros are more distributed than others. Ubuntu, which is clearly the flavor of the month (who says publicity doesn't matter when it comes to Linux?), is out front of everything else, according to DistroWatch. OpenSUSE, PCLinuxOS, Fedora, and MEPIS round out the top five. (Since this is an enthusiast site, one must assume that Novell and Red Hat are way unrepresented, so one should add those guys into the top tier.)
The existence of some number of multiple versions of Linux makes sense, on the grounds that there are different kinds of users who need different distros? But 359?