It was added in 1.8 for the original Kobo. You've probably missed it, it's not really prominently displayed.
Go to your Books (not the I'm Reading List), and "hover" over the book you want to remove. Press menu and at the bottom under Manage should be Delete This Book.
Hope this helps, but if it's locked I'll bet it's some DRM gone awry issue.
Last edited by sunami88; 12-29-2010 at 01:26 PM.