I use this course on my site, and have gotten incredible results using it. The freebie itself is the product and naturally leads in to the sale if you take a few simple measures. Now, if you can't offer a free trial of your product, think of some other way that you can tie the freebie into the sales process. If your freebie itself serves as a reminder to buy it will be quite powerful. Finally, you should always use your freebie to collect the surfer's email address.
Freebies are are crucial in capturing that all important e-mail address.
The way you are doing this with our Search Engine Tactics book is spot on. Use these freebies as an incentive to get people to sign up for your newsletter. Then tie this in with the sales process. I think one more aspect is to keep it fresh. Introduce new freebies as often as you can.