For the discussion: I recently paid for the Synergy software KVM even though it is GPL. Synergy's purchase process is very smooth. Paying $10 for the installers was much easier than compiling it myself. And, I was already had confidence that Synergy was useful, good quality, well-maintained software. So, I was happy to support it as long as doing so was convenient.
Financial Success Stories abound all around. MySQL, WordPress, Drupal, Mozilla (FireFox), Android, etc.
MySQL: Fancy proprietary version with non-GPL features makes money, GPL version sits there doing nothing. Used to make money from a traditionalist dual-license model before Oracle took over, now they just neglect the GPL version.
WordPress: Makes money from hosting and consulting, not from its software.
Drupal: ibid.
Firefox: makes money from search affiliate deals and charitable donations. This is closer because they make money by getting brands in front of Firefox's installed base, which is sort of close to making money from software, but still indirect.
Android: Google does not make money from Android directly except insofar as they negotiate licensing deals with phone providers for their closed-source "Google Apps" suite and/or for "Google Play Edition" or other official branding on a phone. In these cases, they are selling a collection of Android apps and/or Google branding, not the GPL software that runs on the phone.
I don't know of any case where a company sustained itself on the sales of actual GPL software. Every open-source company lives off ancillary services or licensing deals (dual-licensing like MySQL or branding deals like Google).
http://www.redhat.com/en/about/press-releases/red-hat-and-ce...
My favorite IDE RStudio is AGPL which offers a Open Source license that also allows them to charge for added features.
http://www.rstudio.com/pricing/
AGPL - The GNU Affero General Public License is a free, copyleft license for software and other kinds of works, specifically designed to ensure cooperation with the community in the case of network server software. [http://opensource.org/licenses/AGPL-3.0]
I'd be interested in cases where people have made substantial money selling GPL software as if it were proprietary software; that is, where they are able to get the consumer to pay for the software after a short trial, in order to retain the privilege of using the software long-term. The GPL grants this privilege anyway, which is the problem. The consumer doesn't gain any value by exchanging their valuable money for something they already have (the right to use your software), so they don't do it.
For a single app: take a look at what happened when XChat tried to sell their Windows binaries as shareware: http://en.wikipedia.org/wiki/XChat#Licensing