There is one slight catch. The insurance a previous poster mentioned. With Emerald Star anyway, you have to give them your credit card details and they put a lien(?) of Eur800 on your credit card for insurance or if you dont have a card you must give them the money up front. Provided nothing happens to the boat they do not debit your card or will give your money back.
It is a very expensive holiday. The hire of the boat is expensive (although maybe less so if you have a big group hiring a big boat) and the eating out each day is expensive....I don't see the point of going on holidays and giving your time cooking and cleaning up after yourself!
Having said that, we have been twice and loved it each time. My husband is adamant that we go again this year as he refuses to go abroad. We will see how the finances go. I can highly recommend leaving from Portumna and going down the way to Ballina/Killaloe. There are lovely places to stop with nice restaurants. We kept going back to the Derg Inn (can't remember the name of the actual village!), which had great food and a very nice barman who stood us a drink after being back there several times! I have no affiliation(sp?) with the Derg Inn but that was my first holiday with my now husband so it holds particularly fond memories.