Article 14 Border measures
This was one of the most controversial parts in early drafts. It previously would have meant customs could check your ipod or laptop at a terminal and hand over 'infringement' (torrented music, etc) information to copyright holders. Thankfully this part has been declawed, or at least there is the ** opportunity** to do so. I won't go over the parts that apply to chinese bootleggers shipping container crates full of pirated goods, for the little guy:
"Each Party shall include in the application of this Section goods of a commercial nature sent in small consignments.
A Party may exclude from the application of this Section small quantities of goods of a non-commercial nature contained in travellers’ personal luggage."
Okay. So part 1 applies to sending packages in the mail, and even then internationally. If you send a burned DVD of a game or a movie, it can be intercepted and information allowing a lawsuit passed onto the copyright holders. However, a copyright holder has to provide actionable reasons for doing so. Border agents may use 'initiative' to do so on their own, but to be frank I cannot anticipate any state authorising agents to check all international freight; it would be ridiculously expensive. I see this part applying perhaps to known small-time infringers (e.g. someone operating a pirated delivery service on ebay, or at worst a company that burns large media files to disc to send to low bandwidth customers.) Part 2 is where you come in. A concern by some of the signatory states was that they weren't going to rifle through peoples baggage or check their carry-on laptop for downloaded movies. This part allows signatories to do nothing about those issues, and its really a case of watching your national legislature and making sure they don't pass baggage search laws for pirated goods.
Section 4 Criminal enforcement
I'm going to gloss over this part, because it only applies to infringers who do so on a commercial scale. Yes, that means companies like megaupload can be taken down but, as you are probably aware, this part is already implemented in a number of countries in some form. Again, remember that this treaty is for the most part a harmonisation effort to get various jurisdictions enforcing infringement in the same way. This is a personal opinion of mine, but I think that while individual piracy is fair enough, making money off it isn't.
A point of interest is that people who film in cinema halls are directly and specifically targeted by this part.
Section 5 Article 27.4 Digital enforcement (uh oh)
A Party may provide, in accordance with its laws and regulations, its competent authorities with the authority to order an online service provider to disclose expeditiously to a right holder information sufficient to identify a subscriber whose account was allegedly used for infringement, where that right holder has filed a legally sufficient claim of trademark or copyright or related rights infringement, and where such information is being sought for the purpose of protecting or enforcing those rights.
These procedures shall be implemented in a manner that avoids the creation of barriers to legitimate activity, including electronic commerce, and, consistent with that Party’s law, preserves fundamental principles such as freedom of expression, fair process, and privacy.
So this makes the above general part about infringement crystal clear in a digital environment. Of note is that, again, whilst ISPs may be ordered to hand over information on infringers, there is nothing requiring them to gather information to do so, and there is a specific clause " These procedures shall be implemented in a manner that avoids the creation of barriers to legitimate activity " . Which gives ISPs a fighting argument that any new burdens on logging users would be a barrier to their current conduct. The privacy clause is also a strong piece of ammunition for legislatures that actually give a damn about their citizens.
Each Party shall provide adequate legal protection and effective legal remedies against the circumvention of effective technological measures that are used by authors, performers or producers of phonograms in connection with the exercise of their rights in, and that restrict acts in respect of, their works, performances, and phonograms, which are not authorized by the authors, the performers or the producers of phonograms concerned or permitted by law.
Effective technical measures means DRM.
Now this means that a company that creates software that specifically aims to disable DRM is liable for a lawsuit and (remember the criminal element) is liable to criminal sanctions if they do so knowingly for profit.
There are two points to make here :
A great deal of DRM stripping software today is open source of freeware. There is nothing in this treaty that controls the flow of information on the internet, and so long as there is no company or group to take down, there is nothing stopping P2P software exchanging that blu-ray ripper or what have you.
Further, let's look at part 6(b)
(b) the manufacture, importation, or distribution of a device or product, including computer programs, or provision of a service that:
(i) is primarily designed or produced for the purpose of circumventing an effective technological measure; or (ii) has only a limited commercially significant purpose other than circumventing an effective technological measure.
My emphasis. We may as well call that the betamax clause. Which means if there is a legitimate function of the device or software, it will be immune from any actions taken. Again, there is a discussion of what the courts will do here, and how the incorporating laws will treat the issue, but there's nothing to worry about per se from the treaty itself.
Chapter IV International Co-operation.
Well while it won't affect individuals, this part will no doubt help countries co-ordinate efforts against torrent trackers and similar sites. It means that an operation like taking down Megaupload or thepiratebay (from a few years ago), whilst still requiring going to a court, getting the judge to agree and all the rest of due process, will be much easier to put into operation. It means that countries like the US will no longer have to spend months getting individual states to agree to let LEA raid servers; under ACTA provisions, *once the court in one country has agreed, * enforcement can take place quickly.
Summary : How does it affect me?
To be blunt, for individuals there is not a great deal of change, at least if you live in the US (or to a lesser extent the UK). I'm not familiar with the law of the other signatories, but if you frequent reddit, expect similar copyright enforcement standards as the US (the Scandinavian countries are going to

ing love this...)
The dangers are in how the bill is implemented, with the following issues for individuals: Will the enabling legislation require ISPs to keep more detailed logs that can be handed over to copyright holders? Will other legislation (like the child pornography act) successfully pass and not protect the data from non-criminal investigation use? Will government ignore ACTA's opt-out on personal luggage and carry-on goods? It would be monstrously stupid if they did. Will governments shrink the betamax style permissiveness on technologies that can be used for infringement but have other uses aside? For regularly legitimate companies there are the following:
Am I mainly enabling piracy? Megaupload for example. This isn't to say all digital locker sites are in jeapordy; the fairness requirements in the treaty should, if implemented properly mean that sites that promptly remove infringing content are safe. Am I selling things that primarily enable infringement? This will probably mean an end to modchip sellers for xboxes and the like. Heavy criminal and civil penalties mean it will not be a very smart business to be in will I get a betamax exemption for borderline cases? This is what requires careful observation of individual legislatures. If they

it up, things like DVD authoring software could be in trouble.
For companies that almost wholly pirate or facilitate the piracy of goods knowingly.