After having this link e-mailed to me by three separate people, I finally watched the "United Breaks Guitars" video on YouTube.
Summary: United Airlines broke Dave Carroll's $3,500 Taylor guitar. They refused to compensate him. He wrote a song about it, made a video with his band Sons of Maxwell, and posted it up on YouTube.
Where it has 3.5 million hits and counting.
Moral: Don't piss off a songwriter. Ever.