I'm less worried about this scenario: "We are investigating one specific person whom we have probable cause to believe committed a specific crime. Oh look, he has a Gmail account. Let's subpoena his video searches with a valid warrant."
I'm extremely troubled by this scenario: "We don't like people who search for videos on guns/surfing/cats/whatever. Let's subpoena a list of those people and start investigating them on no other basis."
The public needs to create "where do cops live ?" and "what is each cop's collective record on abuse and arrests ?" type databases.
They need to be held to a higher standard that has us surveil them, too.
Watch them; follow them; write it all down.
I've been thinking about a network of private license plate reading cameras that only keep track of known cop license plates.