Now here's some news to get you excited! A huge collection of Irish railway company records, held by the Irish Railway Record Society Archive (IRRSA) is being digitised by Ancestry. I don't know exactly which sets of records are involved, but if they are personnel registers, as I suspect, we're going to be in for a treat.
My grandad worked as a clerk for the railway for about 20 years, and when I visited the IRRSA premises near Heuston Station in Dublin some years ago, I was able to find details (start and end dates of each posting, salary, promotions etc) that saw him, a Tipperary lad of just 15 years of age, start his career at Dungarvan station, then moving on to Maryborough (now Portlaoise) and Bagenalstown, where he met and married by grandmother, and then moved with his growing family to Athlone. If your ancestors spent any time employed by the various railway companies from 1880, this collection shouldn't be missed.
As Irish genealogists will be aware, collections involving several unconnected business enterprises often display a lack of uniformity in the records they kept. Their storage choices may also have been sub-optimal in some locations. Either way, the IRRSA's holding of personnel records is not complete; not all the records for each Irish railway company have survived.
