I'd like to ask people how they heard about NationBuilder during the nation signup process, and a multiple choice custom field would be perfect for that. Unfortunately I can't, as custom fields cannot be used on nation signup pages.
I imagine others would also like to add custom questions to their nation signup process as well.
Thanks Jesse - this is absolutely something that we will consider. There's also a more general suggestion to add custom fields to more NationBuilder pages that you might be interested in!