I though I knew how this work, but, after doing a bit of research I´m really confused. I have a PS3 and a PS4 where I use my regular account. If I bought another PS3 and PS4 I can use that account with those systems, and when I mean use my account, I mean to download my purchase games. So, that will be my limit right? 2 consoles per account. But, what if all those system brokes? I can't download my games anymore? I read something about going to the website and you remove the assing system to your account and you can continue using your account to download games in the future in other systems. So, as long as you have assing just two consoles to your account,it will be ok? Is this true?
As of right now (March 2016), you can have two Primary active PS3 systems and one Primary active PS4 system according to the PSN FAQ page.
You can sign into additional devices and download your games to play while logged in, but as soon as you log out the games become unlicensed for play by other users. I'm not sure how that works with concurrency though... eg, can you play against your self between two systems? IDK.
Note, even this page isn't always current but it's a good guide. For instance you can have three activations across PSP, Vita, and PS TV, not the two listed.