No, Twitter's legal declaration doesn't mean a switch to an all-powerful Irish data protection office.
In fact, Twitter's announcement that it is switching its legal data responsibilities to Ireland is unlikely to affect the activities of our Commissioner much in the short term.
Twitter can say what it likes about where it reckons it is based. But that has little bearing as far as courts or regulatory agencies go. Indeed, this was one of the issues raised in the European Court of Justice case between Google and a Spanish citizen, the one which led to the 'right to be forgotten' judgment. Google argued that because its terms and conditions declared that EU citizens were dealing with "Google Inc" in the US, it didn't have to fully adhere to EU law. The court politely informed Google - and the rest of the multinational world - that European data protection law doesn't hinge on where companies declare they are "based", but where they're active. So if a German, Belgian or Spanish citizen has a problem with Twitter, he or she can start and finish a process in their own country with the full force of European law. In the event that the Irish Data Protection Commissioner gets involved, it is probably only based on good inter-agency relations or a prior informal arrangement.
The irony is that Twitter is one of the least likely to attract much legal or regulatory activity. "Twitter doesn't actually collect a huge amount of personal data," said a spokesman for the Commissioner's office. "It wouldn't be up there with others in terms of gathering information such as behavioural data for advertising purposes." So carry on, folks: there's no immediate change.