But once you factor in getting to and from the airport in Dublin and Cork, it's rarely faster or cheaper.
It's grand if you're connecting in Dublin or if your destination is around Swords, Malahide, Santry etc., but otherwise it doesn't really offer anything better.
However, in terms of the viability of Dublin-Cork as a route, I'd say the fact there is a motorway the whole way between the two cities now has a substantially bigger effect than a train service which is slower than it was a decade ago.