One of the major powers that the DMCA provides to companies, as noted by Greg over at Consumer Law & Policy Blog, is an "easy way for companies to get information taken off the Internet." The way that companies accomplish this is by filing a notice of claimed infringement with the DMCA. The DMCA in turn notifies the ISP with a takedown notice and the ISP usually removes the content or shuts down whole sites which were claimed to be copyright infringing.
Where it gets tricky is that in many cases the 'infringing content' is not actually violating any aspects of the DMCA, but it is typically in the ISPs interest to shut down sites with potentially infringing content in order to avoid a lawsuit.
The other side can be seen here in the case of Diebold Election Systems. In this case the court ordered Diebold to pay court fees and damages to two students and a nonprofit ISP after it was found that Diebold had misused the DMCA in ordering takedown threats when the copyright holder knows that infringement hasn't occurred.