I doubt it will ever come out. Maybe the can't get enough preorders at the price being asked to justify printing it.
Pre-orders is probably the reason. An expensive book that probably cannot be justified during a worldwide recession, and I guess they're looking for a good proportion of a 1,000+ print run to fulfil. But I note the Amazon page quotes a publication date of 2006, which is quite odd. However, publishers will often quote a future date when the book is in progress - has it been that long in development?
The Book Depository also quotes an end-May date.