As part of the Linux Foundation Technical board, we confront the issue of closed source Linux kernel modules all the time, and we wanted to do something that could be seen as a general "public statement" about them that is easy to understand and point to when people have questions.
So, after working on this for a while, and asking some of the other major contributors and maintainers of the kernel, what we have is below.
There is also a site that contains a link to a statement from the Linux Foundation about this topic, as well as some more descriptions and background information, and a copy of the full statement as well.
I've also put a pretty pdf version here in case people want to print it out.
If there are any kernel developers who want to add their names to this statement, please let me know by private email and I will be glad to add it.