Miner username and password - does it need to be unique in the major pools? Every Bitcoin mining pool relies on Basic Access Authentication to identify the user and credit their account for the work performed. But does this identification in form of username and password have to be unique for each separate machine that performs the mining? How is that problem addressed by the major pools?
Usually the worker's username is appended to your account username. So if my pool username is nmat, my workers will be named nmat_rig1, nmat_rig2, nmat_FPGA, etc.

Creating multiple worker accounts is useful to control the performance of your rigs, but is not mandatory to use a different identifier for each machine. You can have all your rigs mining with the same username/password and the money will still end up in your account.