Eons ago, when the legends coded in binary, Jerry Pournelle was forever urging his BYTE column readers to spray something on electrical contacts. It kept some kind of demonic influence at bay.
I thought of him when I recently fixed my wife's Samsung i500 and my battered Palm Tungsten E2*. Her phone wouldn't charge, my Palm wouldn't sync. In both cases scraping the metal contacts with a pin cured 'em. Crud was blocking the connection.
Now that's satisfying ...
* I know people complain about Apple's LiOn battery life, but the Palm battery died when that sucker was about 8 months old!