I work full time in and around Linux on servers, desktops, etc. The best way to use Linux in a desktop is to tune it to a specific job like you'd find at DMV workstations, bank tellers, cash registers, etc. Many of the cash registers you see in dept stores today are already Linux based, like Autozone for example.
Linux like Ubuntu is great for learning about the nuts and bolts of your PC and Linux in general and when someone has the guts they can price a desktop system a lot cheaper.