I've seen Brandon Sanderson do it.
I've also seen James Patterson do it.
And they aren't the only ones.
In my last post, I ripped pretty hard on the whole "free book" marketing technique. However, there is an alternative I could get behind--besides sampling, that is. And it is this: offer a larger sample (say 15-20 chapters) for free. It gives readers a little bigger bite of your story to chew, and at the end, for your call to action, you can direct them to your website, your blog, your author page, or a link to sign up to be on your mailing list.
And, of course, don't forget to have a link so they can purchase the entire book.
I know you still run the risk of readers still not reading the book--I have a pile of free sample chapters by Mr. Patterson I haven't read yet.
Once again, it depends on your marketing plan and writing goals.