From my experience (with BOI, Tesco, Ulster Bank, Littlewood's & Halifax), the Ombudsman Service is a paper exercise. Even the banks know this and have standard letters they issue- it's always great fun picking 'holes' in what they say- but then when it ends up with the Ombudsman, he's inundated and tries to get rid of complaints. Saying that he/ she do great work there- look at their issue with Davy's and Enfield Credit Union as an example.
Saying that, eveni if it is a 'paper' exercise, I would recommend we all complain, when it is deemed necessary. It'll keep the 'friendly' customer complaints sections in the banks busy if nothing else! Also make sure you never put a postage stamp on such letters to them- they all operate 'Freepost'!