Here's a page with information (from "Action of Smoking and Health) about the impact of the ban in Ireland - Impact of smoke-free legislation in Ireland
It apppears the numbers of people visiting pubs after the ban was introduced actually rose. On the other hand, the overall bar sales appear to be marginally lower - equivalent to a 4% annual drop, consistent with a fall in bar sales over previous years.

But the most interesting figure is this: "Polling by independent research company Amarach Consulting found that 89% of respondents believed the ban was a great success and only 10% saying it was unsuccessful. Even smokers admitted that the smoking ban has been a success, with nearly 90% believing the law has worked.