I used Book-It in my classroom teaching PreKs.
Am I a corporate promoter of Pizza Hut? Am I simultaneously promoting bad eating habits to my babies?
I answer no to both questions...but, who knows? Some teachers may be doing just those things.
It depends on the intent.
I use an example from the Bible as an analogy. If I am angry toward somebody else or if he is angry toward me, two things stand paramount: (1) hostility exists between us and (2) we must reconcile. Here's the key: I can go to my brother with as many I'm sorries and olive leaves as I can, but I get no where unless I myself forgive him and if I repent/ask for forgiveness from the Lord. It's the intent and outcome that matters the most, not the means as long as we keep focused on the origin of our intent and if we stay accountantable to those origins.
In the same way, when using Book-It, we as teachers must be mindful of (1) always deferring to what's best for our children and (2) developmentally appropriate practice. In my case, I know that Pizza is bad,...but not in small doses. We do not go to Pizza Hut everyday. It's a special occasion. I love Reeses Peanut Butter Pie and Triple Fudge Chocolate Cake, but I don't eat it everyday. It's like a holiday when I can have it: rare not mundane.
DAP-wise, we should always realize that we should build up all opportunites to keep intrinsic motivation maturation in the child while eschewing as much as possible any external motivation because the later is much better for the child to depend on for success. I do, however, believe that diversity in guidance is necessary just like diversity in assessment techniques--we can't always use checklists and anecdotal records just like we can't always use standardized tests. I see Pizza as a diverse way to reward kids for taking the initiative to read.
That's my two cents.