Now you might notice one catch: namely, that long layover at JFK. And no, you can't get tickets direct out of New York for this price because airlines are lame like that (fares start at $529), so you'll have to deal with the layover. But, come on, you're flying to Ireland for $309!
In addition to this deal, Delta is offering tickets out of Chicago for just $479 and KLM has tickets out of San Francisco starting at $616. And while those prices may sound expensive after the whole $309 thing, they're actually fantastic deals.