Well, to be honest, there wasn't a ton of strategy behind it. I wanted more folks to be able to read the book, so I thought it was a good way to get it into more hands.
I did see a few extra sales, but I have no way of knowing if that really contributed. I used it to essentially create a little online buzz (facebook, twitter, etc.) for the book, and maybe get a few reviews out of it.
One good thing about amazon is the lists by category for free and paid. For a time, my book was next to Fahrenheit 451 on the lists, so that, I think, helps. It was on the first page of free Sci-Fi/Adventure books, which helped too.
There isn't a lot of hard data to review, I'm afraid. Still, it "feels" like a success, and brought me a few more "likes" on FB. It's an ongoing process, that's for sure.