Marie McGonagle, NUI Galway, writes in today’s Irish Times that the judgment in Mahon Tribunal v Keena  IESC 64 (31 July 2009) (also here (pdf)) copperfastens the right of journalists to protect sources (with added links):
… That decision, particularly as it emanates from a unanimous Supreme Court, must … mark a very significant stage in the development … of legal recognition of the right of journalists to protect their sources.
… Mr Justice Nial Fennelly … proceeded to consideration of the High Court judgment, with which he agreed in many respects. There is no doubt that the High Court judgment was valuable, particularly for its examination of the powers and interests of tribunals under the relevant legislation, and of the European Convention on Human Rights (ECHR) Article 10 principles of freedom of expression, including protection of journalists’ sources. Indeed, the High Court accepted that “the non-disclosure of journalistic sources enjoys unquestioned acceptance in our jurisprudence and interference in this area can only happen where the requirements of Article 10(2) . . . are clearly met”. The principle, which had long been denied in Irish law, was, therefore, firmly established.