@conservancy I apologize if I am being too pedantic. I just wanted to be clear.
I agree with others in this thread, and I'll add my 2 cents.
For me, a 501c3 non-profit indicates a commitment and duty to a mission. If a free software project is organized as a 501c3 or is provided services from one (e.g. SFC), I generally feel more secure about the project's priorities and use of resources.
A 501c3 is also the only type of org I would be willing to assign copyright to.