I will likely never find out the true percentages since my family's bee in America since the 1600s, my Dad said I was Irish and Italian but said probably a little German too but mainly Irish and Italian and my family on my Dad's side originated from Ireland in the 1600s but it's hard to tell how much Irish I have in me, because for example, some people aren't white that had their family originate from Ireland, , so I'll never know really it seems.
It's also pretty irrelevant. As far as I'm concerned if your parents were born in country X and you were born there too then that is what you are. I don't see the point in saying you're 50% German, 40% Irish and 10% Moldavian and whatnot just because some of your ancestors were. Not to mention the fact that obviously your genetic heritage gets further and further diluted with every generation and it's not like this happens in clear-cut 50/50 splits or something.
Stuff like that is interesting when browsing through your family tree on a rainy sunday afternoon, but sociologically and genetically it means fuck-all for most people. The exception being people who live in a close knit community with many others with the same heritage that retain their homeland traditions and also marry and breed mostly amongst themselves like the Italian-American community in New York or something. Those people still identify with their "homeland" so much that they would consider themselves Italian even if they are born in the US. That doesn't apply to the vast majority of people in America though.
It's also a negative thing in the sense that it creates a myopic view of the world and makes one far less likely to explore other cultures as well. Of course YOUR culture is so awesome, you spend all your time looking into it while you know nothing about anyone else's culture.
Hey, you're the one cracking down on generalizations wherever you find them!
I'm 100% German, and a German citizen as well as an American citizen. I can always move to Germany if it ever gets dangerous to live in America because of terrorists. Sometimes people ask if I'm Jewish because of my German last name (most Jews have German last names), and that pisses me off.
Sucks to be you.