Here's a solution to a big problem with the Apple headset for the iPhone: the sound level in my headset had become so low, I could hardly could hear a conversation in the car. After some experimentation, I found the solution: high pressure air to clean the earpiece -- evidently the plug was clotted. The same can of pressurized air I use to clean my camera was the solution for my iPhone headset as well. It is now loud and clear again.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20080612055433469