I guess the first question I would ask these individuals is: "How many passports do you hold?"

Persons holding multiple citizenships should be restricted to voting in either their "birth country" or the country they have lived in for the past 5 years (? or perhaps the country where they've earned the most income? ); but not both.

I recognize that the world seems to begetting smaller everyday, especially with the impact of various technologies, and that people are certainly more mobile in their jobs but voting in elections held in more than one country just doesn't seem right.