The bigger problem isn't so much that you've got a 50/50 chance just blindly plugging it in. With all considerations, 50% probability of connecting a device by just sticking your hand under your desk and jabbing randomly with a USB cord is actually fantastic compared to every other connection on a PC.
However, the problem is that the USB ports have no guide to lead the USB in so they stick on the edge and no matter how hard you push it just sits on the edge and makes you think you have it upside down. You would improve usability greatly if the ports just readily allowed the plug to slide in.
I've never had to make an effort to plug in a 3.5mm as the plug design complements the port design. You either miss or it's in.
