The case I talked about in the post below centered around the misuse of confidential informants.  Even scarier is this case which Radley Balko investigated, where jailhouse snitches were used by racist cops and prosecutors to railroad an innocent Loiusianna family.  It shows how drug laws can easily be used by corrupt, power hungry government officials, for the worst purposes imaginable.  It's a long, heartbreaking read, but well worth it.