The new biography to which I think you are referring is Hide-and-Seek with Angels: The Life of J. M. Barrie, written by Lisa Chaney, published by Hutchinson, hardback, 368 pages, ISBN 0091795397. According to Amazon.co.uk it will be available from May 19, 2005, RRP £20, their price £14. Find it on Amazon and there you will see a synopsis.
It is impossible to say, from the synopsis, whether this book will reveal anything new about JMB.
With no shame, I'll use this opportunity to plug my own modest little book, It Might Have Been Raining, which is essentially a small part of my grandmother's life story centred on the time she worked for JMB. It is not quite finished, probably not to be published but available privately through me, probably no ISBN, definitely not hardback, probably ready in April, probably about 100 pages, probably about £5.
My book is not another biography of Barrie. Rather it paints a detailed picture of life with the Barries as experienced at Black Lake Cottage, their summer home. It adds a little detail and colour to the published biographies of JMB.