Since I am an expat European here in New Zealand, the issue of dual nationality has been bugging me for over a decade. In short, my country of birth, Belgium, does not allow its citizens to obtain foreign passports. If you do, you forfeit your right to a Belgian passport and citizenship.
For most Commonwealth countries this is a strange state of affairs. New Zealand, for instance, doesn't give a toss about how many other passports you hold, but the same cannot be said about Australia or the United States.
The issue is essentially one of fairness: if you go live abroad and you adopt your country as a new home, you lose your old passport (with the accompanying loss of voting rights and diplomatic protections), but if your partner lives with you in Belgium and eventually qualifies for a Belgian passport, he doesn't have to give up his old passport.
Now there are rumblings of trying to rectify this unsatisfactory situation, with various bills proposed in parliament and seminars held on the matter. You can listen (not in English) to the parliamentary debate. There is a webforum for reactions and opinions on the issue, and you can contribute in English.
It does seem strange that you lose your birthright by simply emigrating. Presumably if I ever were to go back to Belgium to live and got my nationality back, I don't have to give up my New Zealand passport. That is simply a Pythonesque situation.