Levitt has a blog at http://www.freakonomics.com/blog.php.
His schtick is applying economic theory to social situations. It's interesting and it's controversial, so of course there's a lot to argue with. But stress the interesting part...
As for crime statistics: I spent 9 years in law enforcement and a good portion of my job in the last couple of years (before I left on a medical) was compiling Uniform Crime Reports for the FBI. Local agencies have a lot of leeway in how they classify crimes, and it's quite possible to make crime rates look better--or worse--by the way things are classified.
That said, my experience is that the most dangerous people in the world are young males of any race or social status in groups of three or more. When in a group, adolescent males will do things that they would never in a million years consider doing if alone, and that they are ashamed of later, but the group seems to produce behavior that appalls even its members.
When there's a bulge in the population of adolescents, there's a bulge in crime. When that bulge disappears, crime rates drop. A forty-year-old is much less likely to commit any crime (sociopaths and pyschopaths excepted) than a fifteen-year-old. The reasons are biological as much as anything--not only does the forty-year-old have less in the way of raging hormones, he's also reached the point at which his brain is capable of fulling processing the consequences of his actions--something most teens' brains are physically incapable of.
And that's not based on Levitt, that's based on my personal experience as well as my training at the law enforcement academy, corrections school, and later in educational psychology (after I left the department and went to graduate school).
Before you decide Levitt's full of crap, read him. It's interesting stuff.
Jankyn