Hi soapygal,
To remove a book (or magazine or blog) completely from your bookshelf, click on 'My Bookshelf', click on 'Books' (or Magazines or Blogs), and then click on the little x-in-a-circle over to the right of the title you want to remove [you can verify this by holding the cursor over it without clicking; it should say 'Remove'].
You can also remove a book or magazine or blog while looking just at it and its list of recipes (brought up by clicking on its title in My Bookshelf). Just below the title, you'll see the word Bookshelf with a checkmark, followed by '(Remove)'. Click on (Remove) and it will no longer be on your Bookshelf.
Is that what you were looking for?
Bookmarks don't add or remove items from your bookshelf, they're just personalized ways to group and characterize the books, magazines, and/or blogs on your bookshelf (and of the recipes within them). I believe there's no limit on how many bookmarks you can create and use, even if you're limited to the trial 5-item bookshelf.