Reading a review and getting to the bit where it says, "...and the book will be out in eight months!" does mean there's not always much to say, unless it's the next book in a much-anticipated series and people are fishing for info (and for most such series, you're not going to see a book that far ahead of publication).

Generally I get a lot more feedback if the book's been out for a long time and people are already familiar with it. I'm considering rereading the HARRY POTTER books and reviewing them, and certainly the resulting discussion would be the only real reason to do so (since most people have either read them or already decided they're not going to ever read them already ).