You read that right: the Market now includes a totally awesome Books site. To be honest though, none of us is really sure what all has changed, since none of us really used it before - but it doesn't seem like a lot, other than a flipped switch. Let's start with what it looks like:
Notably, there's now a dropdown to sort by genre (to the left of the search box, above). When you select a book (protip: Sherlock Holmes is free... or if you're like Artem: Walden is free.), you're presented with the option to read it on the web or, assuming you already have Google Books set up and synced, on your Android device.