Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
Although Slackware was THE distro in the mid-90s (which is why I always say it's the best 1995 has to offer), at the present time it has conceded the corporate market (but of course Linux is not about market share, the Slackware zealots always remind me!) to Red Hat and SUSE, and the rest of the market to the many Debian derivatives, with the result that Slackware is now just a niche distro used by a very small minority of Linux users.
Of course, the word "small" is relative here... because I believe the current Slackware user base is in the area of 50,000.... maybe even as high as 100,000.
Unlike Slackware, most Linux distros have by now moved on toward newer and better (IMO) package management systems, as well as either full-fledged GUI admin modules or a collection of easy-to-run scripts that you can use to configure your system. Only in Slackware do you actually have to go in and edit xorg.conf.