What's in a positive review?

I end all my reviews by disclosing how I got hold of the book. I'm told it's important to declare when you've been asked to review a book, and I can see it makes sense--"I received a free copy of this book from the author / publisher / publicist / blog tour organizer etc... in exchange for my honest review." But I add the disclosures for my own purposes too, so I can keep track of which books I "bought" free as a result of good advertising, which ones I was given, which ones I have in real-bo...