The IRS will neither confirm nor deny that they are using such technology. But the Netherlands, Austria, Denmark, Britain and Canada are using it. Mainly it's used to scan online marketplaces and gambling sites to find people who are under- or not reporting their income from such activities.
http://www.wired.com/news/technology/security/0,72564-0.html
http://www.wired.com/news/technology/security/0,72564-0.html