Since March 2004 Irish Government introduced a ban smoking in the workplaces in Ireland. This includes office blocks, various buildings, public houses/bars, restaurants etc. There are usually some smoking areas provided in most pubs and night clubs (usually outside).
If you're a non-smoker or not used to being around cigarette smoke...be prepared for it!
From the moment you step off the plane, you'll smell cigarettes, pubs, bars and clubs...obviously!! You should be ok in restuarants though. It's just a little something you should be aware of!