To contribute to the discussion on space piracy, piracy only occurs when you are sure that you can obtain what you want (i.e. cargo) without it being destroyed, when you are sure that there is little chance of the relevant authorities catching you, and when you are sure the loot can be safely sold without it being traced back to you.
Modern pirates ransom the crew (after beating and raping them, of course), and the ship. A bunch of borderline retarded thugs with AK-47s can't do shit with a freighter, and sure as hell couldn't move the cargo without being caught in the act.
Exactly, which is why I think space piracy will focus more on hijacking and ransom rather than seizing cargo.
To use the example of piracy in the Caribbean, it mainly occurred because of Spanish trade with the New World colonies, and the vast amount of resources that they were bringing back. Another factor was the sheer size of the oceans, Spanish navy ships could not protect every single merchant ship at once. Here, we have a similar scenario, the opening of a new frontier, and the vast amounts of resources brought back as a result. However, unlike buccaneers in the Caribbean, it is unlikely that just any aspiring space pirate possesses the billions of dollars required to build and launch an armed spaceship. It is therefore likely that most 'pirates', in the traditional sense of seizing and selling merchant cargo, will instead be funded by rival corporations wishing to put their enemies out of business, much like how privateering was prevalent in the Caribbean. If new laws are not put down before humanity ventures into space, we could soon see a chaotic mess of rival ships engaging in fights against merchant convoys over the skies of Earth, which would seriously hamper any effort to make progress further into the solar system.
To uses another example of piracy in Somalia, the reason why it remains so successful is because of its simplicity. Just take a small motorboat and some men, arm them to the teeth with assault rifles and rocket launchers, board a ship and demand ransom. The small number of men and the small vessels used makes it easier for pirates to dodge ships of CTF-150. But, as stated earlier, spaceships are expensive to build, which makes it more likely that pirates will be covertly placed into merchant spaceships, disguised as cleaners or other low-key personnel, where they will strike once the ship is too far from help. Again, the number of men needed to hijack a spaceship are very little, perhaps as few as ten to fifteen, which further serves to deepen their cover. What is more worrying, however, is the fact that such hijackings may go the same way as state-sponsored terrorism, with ships deliberately crashing into major political or military installations.
Note: All of the above assumes that spaceships will be few and far between, and the lack of any space force.
Edit: Ninja'd twice!