A new (third) edition of the book on Focus by Australian Peet Johnson arrived through my door the other day - Hocus Pocus: the strife and times of rock's Dutch masters. (See details here) Peet must know more about Focus than any man on earth and this new edition brings you right up to date with facts such as the version of Focus 3 done by Outkast and that by Guo Yue of House of the King (both in 1996). It's a bit expensive but hardcore Focus fans will go for it.