From time to time, I will pick a picture at random that someone posts and strip the XIFF data, and if it has personal ID info in it, I'll tell that person. Really freaks them out!!!
The narcotics departments PAY these guys to do this. You'd be surprised how much info can be gleaned here. Hydroponics shops are even more dangerous! All a cop has to do is sit there and record tag numbers. It has happened to the point of some shops bringing suit against the cops for targeting their customers!!! They don't need probable cause to take down your tag number, find out who you are, then put you under the microscope. Probable cause can then be created by any number of scenarios.
It would take a court order to get posts and info from RIU, and I doubt they'd go that far. But any ISP has all the pertinent info on what URLs are visited by an individual, and they will cooperate with LEO. Just use common sense, don't use a GPS capable camera or phone to take and post pics.
Just don't think that they aren't after the small fish. Small fish are bait for the trophy fish.