Google makes £1.25 billion/year in the UK but doesn't pay any tax because it's HQ is in Ireland, in Australia it makes a loss on $1Bn sales because it's all charged back to Dublin.
MSFT, Dell and HP both apparently lose money on all sales in Europe except those in Ireland.
I'm not arguing that American companies aren't taking advantage of this. All I'm saying is that they aren't just shell companies setup in Ireland. There are Eastern European countries with lower corporate tax rates, if the only reason they were in Ireland was the tax break they would have upped and left year ago. The only reason they are still there is because they actually have infrastructure and campuses.
As far as tax havens go we actually had quite a lot of people from those companies employed, it wasn't just your standard shell company running out of a solicitors office.