I have one, for a mouse. it came from work. A new mouse came with it, and the person who's PC it was for plugged the mouse, compleate with converter, into his PS2 mouse plug. It did not work very well, and he asked me to 'have a look' at his mouse, as it was 'playing up'. I turned his PC off, plugged the mouse, minus converter, inot the USB socket, and the problem was solved.
The moral is, they don't seem to work very well.
Have heard this also from a friend who works for a software company. They chuck them in the bin when they arrive with keyboards/Mice.