Its from a tag in the Royal Armouries museum, Leeds, UK, that i vistited that the information comes. They have there a Japanese xbow, and the tag said that the few of them (including the one in display) were kept in the Tokugawa (the Shogun) castles just for show and that they were imported from the Westerners. It said that they never were used in battle. The xbow itself seemed to coroborate the account: it was too well decorated to have been a battle weapon.

I also have read/own a book, called "Secrets of the Samurai" (http://www.amazon.co.uk/Secrets-Samu.../dp/0804816840). It does reference all weapons techniques from the Nara period (10th-11th century) to the Tokugawa Shogunate (1615, end of 19th century). Xbows are not mentioned as a battle weapon in Samurai warfare. I doubt its because of conservatism because they did adopt gunpowder weapons.

That's my sources - i am pretty certain about it - but of course i could always be wrong.