Hackers: They do things because they can, regardless of the actual utility of the project. Case in point, adding support for a PC mouse to Sony's handheld PSP.
Crafted by a German techie, the hack combines all the portability of the PSP with the completely stationary platform requirements of a mouse. In essence, it doesn't make much damn sense.
As the below footage detailing the project shows however, it does make playing first-person shooters much easier.
I won't claim familiarity with the technical wizardry employed to rig this thing up. Instead, I'll let SlashGear explain how it was accomplished:
It's not USB at all that connecting the mouse to the PSP. Instead an old PS/2 mouse has been used, together with the PSP's serial port. A quick breadboard with the ATMEL ATmega8 chip allowed him to write up some code for the PSP; it eventually connects via the PSP Slim Remote.
All of the mouse buttons work, as does the scroll wheel, and there's even adjustable scaling and sample rates. You can map different PSP buttons to the mouse's controls, too.
Dubiously useful? Completely unnecessary? A waste of free time? Maybe, but you can bet that the millions of professional Coded Arms players around the world are going to want one.