Those 98 walks per 162 games are scary. I'm curious to what will happen when his stuff begins to decline. I don't think he'll be able to compensate for the number of missed bats he was generating.
Plus, his shoulder's probably going to fall off. He's only 26 years old, but he's thrown nearly 1450 innings in his career. Christ, that's a lot of pitches for a guy that young.
He finished fourth in number of pitches thrown in 2006, he would have easily finished 1st, had Arroyo, Harang, and Zito had comparable innings. (24, 16, and 7 respectively)
Zambrano is a great pitcher, but I don't think you're going to get a great return on investment on this guy.