Most publications that publish book reviews--especially those that publish daily, weekly, or monthly--seek reviews of new books only. Of course, the definition of "new" can vary. Some less frequently published literary journals will review books published within the past six to twelve months; if you read your local newspaper's book reviews chances are only the most current releases are getting any attention there.
New book reviewers often want to know how (and where) they can find out about new books. They're especially interested in finding out how to locate books that haven't yet been published--this gives them the time to pitch a review, secure an assignment, and write a review that will indeed be "current."
There are lots of ways to go about this--and I cover them all with the writers who study book reviewing with me. But this morning I learned about a new resource that will interest poetry book reviewers in particular. It's a list of spring 2006 releases compiled by the Academy of American Poets. Check it out here.