According to this c|net article, on Thursday, London-based market intelligence firm Mi2g said that the worm caused between $950 million and $1.2 billion in lost productivity in its first five days worldwide. That puts the worm at No. 9 on the company's list of the most costly malicious code, behind the likes of the Code Red worm, with its average of $2.6 billion in productivity loss; the LoveLetter virus, with $8.8 billion; and the Klez virus, with $9.0 billion.
And you wonder what systems the majority of these viruses are infecting :P