It's an "inspired" history of Hitler's fascination w/ the occult, although I think it contains much useful information. For example, it ties in the Parsival myth w/ the Holy Grail and medieval secret socities (like the Templars). It also provides a fairly comprehensive who's who of 20th century germanic occultists (including Crowley).
The spear in question is the so-called Spear of Longinius, the Roman Centurian that pierced Christ's side on the cross. It is a currently a part of the Hapsburg Crown jewels kept in a Vienna museum. It supposedly has cosmic powers to effect world history and so was immediatly confiscated by Hitler when the Nazis took over Vienna.
The Catholic Encyclopedia says the this particular spear (in Vienna) is not authentic, although Hitler certainly thought it was.
In any case, Ravencroft's exploration of the occult in Nazi germany is the best (admittedly esoteric) that I've seen.
I did a little surfing around on Amazon.com and "Spear of Destiny" seems to be discredited to some degree. The most scholarly book seems to be "The Occult Roots of Nazism," although I don't know much about the subject.
The story about Hitler running across the spear in his youth and his being fascinated with it seems believable to me. This seems to be consistent with an artist personality type, considering that he was a frustrated artist in his youth. (I can say this because I'm an artist by trade, and hopefully an exception ;o)
I'm sure the Vatican probably has it squirrled away in some musty, dusty old storage room somewhere.