Good post but I'm curious about this. You are already working on two products which haven't launched - why did you decide to add a third task of writing a book? Would it not have been better to launch the products, see if those signups converted to users, and then write the book?
But since it is just the two of us, and I'm the only one who can work on backend code, Joelle has some open time. She is doing much of the early work on the book while I push product (currently focusing more on Minimalytics to get the first beta open).
As for waiting to see if the signups convert to users...I think that has more to do with the traffic sources versus the techniques being taught in the book. I wouldn't want to wait months when the inspiration has already struck and is fresh :-)
And re: YouTube...I watch plenty of YouTube videos by people I would never give my email address to. I also give my email to alot of people I would never buy from. It's a numbers game.
And 1,100 email addresses is a huge number for us, and for many people who have fewer than that on their list. We spent years wondering how to build a list of engaged folks, so when we hit on something that resonated...we knew it was a big deal :-)
It's also a lot of validation that the core concept he communicated is worth pursuing. If he put up a landing page, promoted it, and got no email addresses, that would be a signal in the other direction.
1,100 email addresses from people to volunteered them in response to your idea is nothing to shake a stick at, especially in such a short period of time.
And frankly, most pages built that early in the process are awful considering all the unknowns.