I just got back from a business trip to Dublin, Ireland. While there, I had the pleasure to enjoy a vast quantity of Guinness. I've always heard people say that the Guinness in Ireland is so much better than what we get here in the States. I would have to agree wholeheartedly. I think there are several reasons for this. First, the Guinness in Ireland is simply fresher, but I'm not sure that alone is sufficient. I also heard (no idea if this is true) that the Guinness brewed for export to the U.S. is brewed in Nigeria. If so, that changes two important ingredients (this applies no matter where it is brewed, except in Ireland). First, the water source will be different. Being a home brewer myself, the mineral content of the water can have a direct affect on taste. Second, the Guinness brewed in Ireland is all brewed with Irish hops. I suspect that the hops used in Nigeria (or whatever) would be imported from Europe and is simply not the same.
After having sampled the Ireland Guinness, I did have a Guinness (or three) at my local bar last night. It was clearly inferior to the Ireland Guinness, but even then, the Guinness here is still a damn good beer.