This is how game sharing works:
I buy Games X, Y, and Z on my PSN account. I give you my login info and you create a new user on your PS3 and log in as me. You can now download everything I have bought to your PS3. As long as you leave that user account on your system, you can play all of that stuff. So thats 2 activated systems on my account. I can give my info to 3 more people before I hit the limit.
That doesnt stop you from downloading and playing your stuff. The problem is if you get a new console since you cant activate any more systems. So you'll have to deactivate someone. I'm not sure if you can do it remotely from the website, but if not you'll have to have your friend do it themselves. Hopefully they remember to do it before their PS3 dies or they sell it or you may be stuck.