Seeing as the medium of "the chat room" has been pretty much around for ten years, I would have thought the cops were there already:

Police in the UK, US and Australia will make use of the different time zones to monitor the web 24 hours a day. If a dialogue is potentially dangerous, officers may warn both online parties. The National Crime Squad in the UK and the FBI in America are heading the effort to set up the full-time surveillance. They are both involved in the Virtual Global Task Force, along with US Customs, the FBI, the Canadian Mounted Police, Australian Federal Police and Interpol.

In the mid-90s when the analogies were flying around for what the web was and what etiquette and other behavious levels were appropriate, I accepted that it is like walking in a crowd on a busy city street. If I said anything out loud in that context and was nabbed by the coppers, I'd have no expectation of privacy to defend myself with. A chat room is no different.