One of my dad's friends is Filipino, and lives with her husband (my dad's best friend, really obviously Irish-American) in the Philipines, so I'm a little more knowledgeable than most. And most of the Spanish-speakers around here are Central American, so my immediate thought is rarely Mexican.

Well, with caucasians, I think most of us tend to be mixed enough that you have to go by names - there are certain features that are Italian versus British versus Scandinavian verus Eastern European, but it's hard to tell. I've got a really British last name, though, and to draw examples from various people I know, there's Zukic (Bosnian), Kriese (German), Romano (Italian), Duffy (Irish), Sliwoski (Polish), and Johannessen (Swedish). Half the people don't look really specificly one thing or another, but the names are telling.