For the Sony software, the maximum # of devices that can be activated is 6. This includes computers and readers. If you are no longer going to be using a reader or computer, it's a good idea to deactivate it prior to getting rid of it if possible. That'll free up one of your activations for another device.
For Adobe Digital Editions, I don't know if there is an exact number. And deactivating a device is not as straightforward as it is with the Sony. Jim Lester who posts here from time to time and I believe works for Adobe has said that Adobe's approach is to simply add more allowed devices over time to take into account users switching out computers and readers.
dordale
