There has been little guidance from the courts in Illinois about electronic discovery. The Illinois Supreme Court has changed the rules a little bit to accommodate electronic issues. But for the most part we treat electronic discovery the same way we treat paper discovery. Facebook posts are discoverable to some extent and get used in the courts. Electronic documents are discoverable under the discovery rules.
The appellate courts are slow to get cases because unless a litigant wants to take the time and money fighting about it the issues frequently just get resolved at the trial courts, without appellate review.
However, the appellate court recently got a shot to make some law in the case entitled Carlson v Jerousek 2016 IL.App (2d) 151248. The case got to the appellate court in the normal way for a discovery issue. The plaintiff took a friendly contempt after the court ordered him to comply with its order. The court had ordered that the defense could do a forensic image of all his 5 computers.