Apple has been caught blocking the use of Dtrace for its iTunes product.
The block was found by a Sun blogger, Adam Leventhal,
here. It seems that Apple felt that while Dtrace was a useful product for other people's applications it was too egalitarian for the classiest sensibilities of its own products.
Of course, Leventhal and his other Dtrace fans have already worked out a way around Apple's blocking antics and published them for the whole world to see.