Only three Irish Universities are in the first 500 - Trinity College (rank 236). University College Cork (rank 458), and University College Dublin (459). My current employer, the National University of Ireland, Galway does not make the first 500 places (whereas Stanford, USC, and Karlsruhe do). The reason is not very hard to find - the ranking ist mostly based on research results and reputation, and NUIG has only started the transition into a research university.
However, the level of funding and activity inside NUIG is increasing - examples include the centers DERI and REMEDI, Alan Ryders' group or the National High-End Computing Centre, directed by Andy Shearer (all of them funded by Science Foundation Ireland), which increases the pressure on NUIG to transform itself into a service-oriented research university. The transformation naturally puts a lot of stress on the system and it is not without pain on every side. But the university is changing and more and more emphasis is given to research excellence.