Living in Dublin we have gotten well used to the smoking ban and it doesn't bother me, a smoker at all. It is amazing how quickly you get used to it. The only downside is the new smells you get in the pub i.e. B.O,farting etc.
Most pubs have security controlling the smoking areas and i've yet to come across any rucks happening, most lads reckon it's a great way to meet birds infact.
Most late night places that are not allowing anymore new customers in will stamp the hand of a smoker on their way out so they can be easily distinguished from people chancing their luck to get in.
Basically you will need people/security to monitor people leaving and coming back in.
Hope this may be of some use.