I moved from Dublin to San Jose almost two years ago.
Apart from the many many cultural differences, I think overall "the valley" is a better place to live & work for people at this time - don't have time to go into detail, but the great weather, shear number of startups & startup events / support and community here is hard to beat, feels like everynight there is something going on relating to startups.
Also the ability to attend various meetups and hear directly from big name CTO's and lesser know but often equally smart developers offers a great learning experience.
The cost of living here is ridiculously low compared to Ireland.
When you get stressed Tahoe is only a 3 hour drive away :-)