Drinking Guinness may be a close approximation to heaven, but something people often ask me, as I'm an Irish person living in England, is:
"Does it really taste different at home?" And the answer? Yes, yes, yes, unbelievably and subtly so!

Irish Guinness, which is brewed in Dublin tastes crisp and clear (whether it is the extra-cold stuff or not), a touch more bitter and tart than the English version (which is brewed in London). Additionally, Irish Guinness feels smoother in the mouth and can certainly be downed more easily (not that I advocate the practice).

On a recent visit to the Dublin brewery, I asked what the difference between the two is. The answer explains the above mentioned differences perfectly: Water. In Dublin, the Guinness is brewed using water from a Spring which occurs naturally somewhere near the brewery. In London, the Guinness is brewed from good old Thames Water (not from the river, the stuff the "Thames Water" company pumps down the mains). Since it is an oft-quoted, but no doubt apocryphal saying that the average molecule of Thames Water has been through a Human body eight times since it last was in the Sea, I will rest my case.

To add my two-pence worth, the best pint of Guinness I've ever had was served in my local pub.