BlackBook.
Though I find it hard pronouncing the capital B in the Book bit. It comes out just like a lower case b would sound. But so does the B in the Black bit.
Maybe it's because though I write the name as "BlackBook", when I say it, I'm actually saying Blackbook or even blackbook.
The iMac is called the iMac, the iPad - iPad, and the white macbook is referred to as "the mac" or sometimes "the white mac", or even by my dear wife simply as the laptop, though that does send a shiver down my spine.