Recently I read a book, Swoon, via Barnes & Noble's Read In-Store feature on the Nook. Basically this allows you to read entire books for free while you're in the store. You only get an hour per book per day, but you can read the entire thing for free that way, and not just a sample.
In general, I found Read In-Store to be a great feature, one I plan to use regularly from now on. There are a few drawbacks, of course — you can't change the font style or size, or use bookmarks, notes, or the table of contents. Also, it counts each Nook screen as a page, which gives you almost double the actual pages. However, it will remember what books you read in-store recently, and take you back to where you left off last time.
I do recommend that if you plan to buy the book, you stop reading at the end of a chapter, to make it easier to find your place in the book. The Nook will not remember where you were if you switch from Read In-Store to a purchased copy, and since the pagination is all screwed up, you'll have a hard time finding where you left off.
Another drawback is that the Nook downloads each page from the server every time you advance one page in the book. This means two things: 1) You are dependent on the Internet connection, and 2) The wireless on your Nook has to stay on constantly, which drains the battery much faster than usual. I did encounter some problems with the next page not loading, but found that if I accessed the book from Shop > Recently Read In-Store > [book title] instead of getting there via Reading Now, the problem generally went away.
Despite the drawbacks, I loved using the Read In-Store feature, and plan on always reading something in the store. It took me a couple of weeks to get through Swoon, and of course since I could only read in the store I often had to wait to see what happened next; but for books that you think you might not want to spend the money on, this is a great option.