The IPAs have your username embedded and can be authorized to be used on up to 5 devices.
You can dump your apps into another device not registered to the same account, but it's going to want you to enter the password every time you try and install an update.
iOS devices can only use a different username every 60 days as far as I understand it. You can get by this limitation by doing it on your computer instead.
My brother and I used to do the sharing thing until iCloud came about. I would advise people against doing that these days because people have so much trouble deactivating it without multiple hard resets.
There is a way to do this stuff with a jailbreak, but that is not a suitable discussion for MobileRead.