We're in the middle of putting together Traction (the book), and have been experimenting with different email auto-responses when people sign up for the mailing list.
Our best results are with this email:
To: $emailSubject: Traction Book QuestionThanks for signing up for Traction book updates!We're in the thick of it right now, and would appreciate your reply all to the following question:What question about Traction would you most like answered?Gabriel, http://ye.gg/
We tried asking a few questions at once, but this one-question setup has worked the best. We also tried framing the question differently -- the shorter and more direct the better the results.
We get about a 20% response rate!
And more importantly the responses are useful. They're helping us shape new content and present our existing content more effectively (as we continually edit).
Also, the whole process is engaging. Justin or I respond to everyone who writes in, usually offering a link to something that may be useful and commenting on whether or not we will answer the question more in depth in the book.
I recommend this concept of the poll auto-responder.