Actually, what I linked to is an attorney's post giving direction on how to properly subpoena social media sites.
Anyone can subpoena records from social networks. The links provide contact information for issuing subpoenas. I am a paralegal who has subpoenaed MySpace, FaceBook, Yahoo Groups, and other sites in cases. You do not need to be in Law Enforcement. I know all too well how easy it is get this information.
Not only that, but a paralegal working in a law firm can "Print Screen" a post, draft a declaration, and attach the document to a pleading to be used as evidence. Something I have done also. I have been in court to testify that the "Print Screen" image is accurate. Most of the time, the poster does not object because they know it is an accurate representation.