Like Edinburgh, the proposed trams for Dublin, Luas, met with widespread objection. People argued that the system could not work in traffic, would take a long time to build and would cost the taxpayer a huge amount of money. The system did take three years to build and, in the street-running sections, caused considerable disruption.
However, Luas has been a massive success and is currently the only transport system in the country which does not require Government subvention, due to huge traffic levels. Thus, the great performance of the Luas saved the government 2.5 million euros. There are two lines - the Green line from St. Stephen's Green to Sandyford Industrial Estate runs mainly on a former railway alignment while the red line, from Connolly Station to Tallaght, has street-running in the city centre.
Both lines carry 60,000 people a day (2005 figures), taking a considerable amount of traffic off the roads. An extension to the Green line was started in May 2007; there are plans for extensions to both lines, and to connect them up (they were supposed to connect in the original plan but this was abandoned due to pressure to build a metro). If you want an idea of the disruption caused by tram construction, please visit the Luas section of my site:
http://www.hidden-dublin.com/images/thumbs/luasTN02.html
You will also find some movies with driver's eye views of the complete lines!