I knew these sorts of lists were kept, but was still disturbed to come across this specific one today. Someone has taken the list of everyone who had contributed to support California's Marriage Amendment, Prop 8, as of early October. The list is conveniently sorted by state and then city to facilitate the research.
This list is an attempt to determine which contributions were from Mormons. But such a list could easily be used to blacklist anyone who contributed in one's community.
Notice the careful way the have framed this as mere information gathering. Can you imagine what the GLBT activists would be saying if a comparable site was set up with the full list of donors for the campaign against Prop 8?