The specifics of the treaty are being kept secret from you, despite efforts to reveal information about it. Even FOIA requests have been stymied, due to 'National Security'. Thank you, Black Jesus. In case you didn't know, it's not on par with snitching, but denying FOIA requests is fucking bourgie. Here's what was released.
tl;dr The following is what we've been able to learn so far.

You have 10 seconds to comply.

ACTA member countries will be required to provide for third-party (Internet Intermediary) liability. This means ISPs will face heightened liability for websites that even link to allegedly infringing content. Websites would have to proactively police copyright on user-contributed material. This means that Flickr, YouTube or even our beloved ED would have to employ a phalanx of lawyers to ensure that the mountain of material uploaded every second isn't infringing on anyone's copyright. Or they could just shut down. ISP-level content filtering could boil down to spiders that scan and check your hard drives to ensure copyright compliance.

One of the more aggregious aspects of the ACTA is it's MPAA-sponsored Three Strikes amendment, wherein a user would face a year-long ISP-level ban after being accused of infringement three times by a copyright holder. No evidence would be required, only suspicion. See: DMCA trolls wet dream

The whole world must adopt US-style "notice-and-takedown" rules that require ISPs to remove any material that is accused - again, without evidence or trial - of infringing copyright. This has proved a disaster in the US and other countries, where it provides an easy means of censoring material, just by accusing it of infringing copyright.

Standards to be Employed by Customs for Uniform Rights Enforcement (SECURE) is the provision that requires customs officials to enforce international law. Now instead of just the usual cavity search for WMDs, you can fork over your iPhone and your Zune. Just kidding, no one owns a Zune.

“	The treaty suggests that customs officers should be given the right to search laptops and media players for pirated material.	„
—RTE magazine

Now, before you start twisting us up a tinfoil dunce cap, check out what's already on the books. The treaty would increase pressure on publicly paid customs officials to enforce what is essentially a private civil matter. Instead of paying their lawyers to go after copyright and trademark infringers, they're sculpting legislation to make the public pay for it.

“	PURPOSE. To provide guidance and standard operating procedures for searching, reviewing, retaining, and sharing information contained in computers, disks, drives, tapes, mobile phones and other communication devices, cameras, music and other media players, and any other electronic or digital devices, encountered by U.S. Customs and Border Protection (CBP) at the border, both inbound and outbound, to ensure compliance with customs, immigration, and other laws that CBP is authorized to enforce. These searches are part of CBP's long-standing practice and are essential to enforcing the law at the U.S. border. Searches of electronic devices help detect evidence relating to terrorism and other national security matters, human and bulk cash smuggling, contraband, and child pornography. They can also reveal information about financial and commercial crimes, such as those relating to copyright, trademark and export control violations. Finally, searches at the border are often integral to a determination of admissibility under the immigration laws.	„
—U.S. CUSTOMS AND BORDER PROTECTION, CBP DIRECTIVE NO. 3340-049 credits to ED