The final straw was noticing a comment referring to "the most recent survey I know of" and realizing it was from May 2009. I think it is well past time for another survey, so here is one now.
I've tried to keep the structure of the last survey intact so it will be easy to compare results and see changes over time, but there were a few problems with the last survey that required changes, and a few questions from the last survey that just didn't apply as much anymore (how many people have strong feelings on Three Worlds Collide these days?)
Please try to give serious answers that are easy to process by computer (see the introduction). And please let me know as soon as possible if there are any security problems (people other than me who can access the data) or any absolutely awful questions.
I will probably run the survey for about a month unless new people stop responding well before that. Like the last survey, I'll try to calculate some results myself and release the raw data (minus the people who want to keep theirs private) for anyone else who wants to examine it.
Like the last survey, if you take it and post that you took it here, I will upvote you, and I hope other people will upvote you too.
For a formal argument about descriptivism I'd agree with your "should". I disagree for a throwaway joke playing (as far as I can see) on an implicit understanding that descriptivists often go out of their way to rebut undue prescriptivism. (But I guess this is a side debate about our personal thresholds for jokers making a punchline land by relying on a word's connotation instead of its formal meaning.)
I might be misunderstanding something, because I think you're only correct given particular, narrow meanings of e.g. "improper" & "mistake". People often use words like these in another way: to make prescriptive claims that simultaneously put forward and rely on (whether explicitly or not) descriptive claims that can potentially be refuted by another descriptive claim. If I say "'ain't' isn't a proper word", I could mean a number of things. I might mean that "ain't" shouldn't be used because it connotes low status tout court. If so, pointing out a dialect or subculture in which it indicates high status would refute me. I might mean that "ain't" shouldn't be used because it's a neologism. Pointing out that it's an old usage would then refute me. I might mean that "ain't" shouldn't be used because it's difficult to understand. Survey data showing that most language speakers readily understand it would then refute me. These would be examples of refuting a prescriptive claim with a descriptive one.
Sure, strictly these aren't direct refutations of the prescriptive claim. But in practice some prescriptive claims live or die on the basis of some falsifiable descriptive claim. I suspect most prescriptive claims made by everyday people do; prescriptions that are just bald assertions are harder to defend.