It contains a lot of copyrighted content, especially ebooks and software. This could be avoided if they would just follow the rules like everyone else.
Nearly every large service that allows user uploads contains a lot of copyrighted content, hence DMCA safe harbor. IA seems to operate in a gray area with stuff like the Console Living Room (which doesn't allow downloads), but as far as I've heard they are responsive to valid DMCA notifications. A lot of supposed "DMCA notifications" are bullshit, though (don't contain the required elements, not sent to the registered DMCA agent).