According to a couple of friends who work for Bloomsbury the manuscript of book 5 has not been delivered by JK Rowling. There were some issues about whether it was to be released last Christmas (in conjunction with the first movie) or this summer, but it's become a moot point - the fact is it hasn't been finished yet, and the publisher's don't know when it's going to be ready.
The last I heard was that if they had the manuscript by the end of June then they were hoping for a surprise release in September - but it's almost the end of July now, and there's still no sign.