Ireland fears the punitive terms of a bailout as it would have to give up partial sovereignty over its finances and could be forced to raise corporation tax.
The story is here. Note that casting your financial lot with the EU is especially problematic if you don't expect the EU to be so influential five or ten years down the road. Obviously the Irish are betting against the idea of a major step toward EU fiscal union and correctly so.
Addendum: Finland weighs in.