I have to say this has been a very interesting thread and it does ask some questions I have been wondering about as of late as well. First I would like to say that up til this point all software that I have written to run on Linux is on a freely useable license, therefore I feel that I have contributed to the open source movement, these include various emulators, games, and development tools and libraries, all are not necessarily on the GPL but much closer to the BSD license, I have granted free rights to modify and distribute so long as it is not used for comercial use.
But at the same time I do have to earn a living and I have decided to take one of my previous open-source projects and enhance it with the purpose of selling it. The original version will remain freely available, only the new one will be closed. I know I do not run afoul of any of the licenses since the only library I use is libc, everything else in my projects are my own libraries, but at the same time over the years I have benefited from the open source model (not financially, but availability of a solid platform and development tools) and I feel that I have given much back in that I have distributed most of my software on an open-source model. Would I still get the evil eye from the OSS world under this circumstance??? What is the opinion if most of my software is open-source and 1 or 2 projects are not???