At the risk of a proper lambasting from the commercial pilots here, I feel that a Practice Pan IS something that GA pilots should do. Please remember that you guys use the radio all day long and are used to it. Some GA guys, although perfectly good pilots, are not used to transmitting on a radio and become self concious that everyone can hear them. I myself don't have a problem, and in the past have been accused by instructors of sounding like a commercial pilot (nothing wrong with that for my money) but for those that are not totally at home with the radio it can seem a daunting place to be. If the wheel is coming off the last thing you need is to be worried about making a call to controller in D&D incase you "fluff your lines", therefore a practice now and again not only might give a bored controller something to do, but also means that the pilot is familiar with speaking to them, and when the day arrives when it's for real will feel more inclined to call them whilst the problem is still that, a problem, not an incident!
Finally, although we do appreciate the fact the the commercial guys monitor 121.5, it could help by relay if we are out of range, please don't appoint yourselves to role of guard police. If you have a problem with someone using the frequency for a practice then report it through the proper channels, son't launch into someone that might be scared of using the box in the first place!