The verdicts in two US trials are being appealed against because jurors made comments about them on social networking sites.
Defence lawyers in the two cases say postings by jurors on sites like Twitter and Facebook could be grounds for appeal.
Jurors are forbidden to discuss anything relating to a case outside the deliberation room.
But experts say the emergence of new technologies is challenging the rules.
In one case in Philadelphia, lawyers for Democratic State Senator Vincent Fumo, who was found guilty on corruption charges, are appealing after juror Eric Wuest admitted posting comments about proceedings on the Facebook site, saying they were his private musings.
One of his messages told people to expect "a big announcement on Monday".
The defence called for his removal from the jury, arguing that his comments "tainted" his judgment, but the judge allowed him to remain to deliberate.
In a separate case, a building materials company in Arkansas, which had been ordered by a judge to pay out $12.6m (£9m) to its investors, has appealed against the decision, claiming that a juror was posting messages relating to the trial on the microblogging site Twitter.
Russell Wright and his company, Stoam Holdings, allege that juror Jonathan Powell sent eight messages to the Twitter site from his mobile phone, including one which read: "Nobody buy Stoam. It's bad mojo and they'll probably cease to exist, now that their wallet is 12m lighter."
Stoam's lawyers argue that the messages show that Jonathan Powell "was predisposed toward giving a verdict that would impress his audience".
These two cases raise questions over the use of social networking sites.
Some legal experts say that the courts system is not designed to work in the "wired" world, others argue that online commentary should be treated no differently from things that are said in person.