I think it's great news that there is finally a second low-cost airline to be launching flights from Dublin, because whilst Ryanair's fares are usually competitive, the lack of mainland European destinations served from DUB, whilst admitedly increasing, must make it more difficult to have a second property abroad than it is from the UK, due to the lack of cheap flights to destinations like AGP, ALC & FAO. Correct me if I'm wrong, but until recently AGP & FAO were only once weekly by FR.
Although my problems with the JetGreen model, is that firstly they're using a two-class cabin, which hasn't worked for most no-frills airline, besides AirTran in the USA, and secondly that they're using the 757, which cannot be turned in under 55 minutes. Surely, with the extra time it takes on the ground, meaning less utilisation, its costing JetGreen a small fortune. It means that there's no chance of any short hops to pad up the schedule, like Go did in the early days of their Malaga flights ex-STN, they mixed it with a quick hop up to EDI.