I lived in London for 10 years in the 90s and overall, I had a good time there. Having said that, it was never home however and I was always conscious ( it reduced over time), that I was an outsider in another country. In hindsight, going there was the one of the best things I ever did because I learned more and developed my career more then I would ever have done in Ireland. The best thing I ever did however, was to come home after then 10 years.
From a practical persepctive, with the income levies now in place in Ireland, the chances are you will pay lower tax and the basic cost of living is lower then in Ireland, especially outside of London. However transport costs, council taxes, water rates and the money you will spend flying home for weddings/funerals/holidays/matches etc etc will negate any tax savings. Depending on your commute, you could easily spend £2-3k a year on train and council tax alone.
Bear in mind VAT will rise by 2.5% in Jan 2011 as well