A nice example of overlap between the virtual world and our physical world is this story told by the NYT: the use of real world detective to find virtual world spam.

Sterling McBride spends a lot of time waiting for spammers to make a mistake. (...) When he hunted down escaped prisoners for the United States Marshals Service, Mr. McBride learned the value of lying low until fugitives trip up, leaving small clues on their whereabouts. Now, as an investigator for Microsoft, Mr. McBride watches carefully for tidbits of data that link some of the two billion pieces of junk e-mail that Microsoft's Hotmail service receives each day with the people who send them.

Once he finds an electronic key to the spammer's identity - a real name, address or phone number - Mr. McBride uses all the tools of a regular detective: trailing suspects, subpoenaing their bank records and looking for disgruntled former associates to become informers. But first he must lift the cloak of anonymity provided by the Internet.