Not at this time, but this is one of our higher priority items to add to the site - the ability to tag books.
We are going to allow custom tags. So if you want to track all the books you own, and want tags stating "ebook" or "hardcover", you'll be able to tag them as that. If you want to tag books where they are located in your house, such as "Bedroom bookshelf" or "Basement bookcase" or even tag books such as "Lent book to Steve" then you'll be able to do so.
So it is coming, and is on the priority feature list.