When I LOVE a particular book, particularly one that I think isn't getting enough exposure like Paty Jager's Spirit of the Mountain or Inez Kelly's Sweet as Sin, I do a blog post (making it my pick of the week if I can) and a Goodreads review AND Amazon and, occasionally, Barnes and Noble.
It's the heart of what I want to do as a reviewer--getting great books more exposure, and I throw my whole self into it. On the other end of the spectrum, I very rarely do reviews of books I don't finish at Amazon/Barnes & Noble--I'm not going to tell readers to NOT purchase a particular book as for all I know there are legions of people dying for the purple-goat story. I see Amazon/Barnes Noble/other bookseller reviews as telling readers whether or not a particular book is worth their money. This why it's so important to me to identify which types of readers a particular story may work for, because worth is so darn subjective.