This is one of those terminology issues. Officially, you can only have the item in question (if purchased after the policy change) on two systems. However, you can download it to more systems than that, it just won't work on more than two at a time. Your PSN account keeps track of what systems you have used your account on, an at any one time, now, only two systems can be "active." This will allow them to access DLC, PSN games, etc. You can change your active systems at any time though, most easily though the actual PS3 itself (Account Information, Activation), but also through a computer (1 time every 6 months), which you can find instructions on here:
http://community.us.playstation.com/t5/General-Discussions-General/How-To-Deactivate-PS3-PSP-via-PC/td-p/36478641Now, this works for game content. I'm not sure how it works for the video side of the PSN. Also, doing it through the computer will deactivate ALL of your PlayStation systems from your account, so you would have to go back and re-activate the ones you want to currently use (not only PS3s, but also PSPs and/or Vitas). This can be as simple as going back into the Account Information settings and re-activating, or usually when you download a title/DLC, it'll try to auto-activate the system.