US Opinion on Dual Citizenship

Direct from the State Department:

U.S. law does not mention dual nationality or require a person to choose one citizenship or another.

Via the US Embassy in New Delhi we have:

The Indian government recently launched a program called "Overseas Citizens of India" or "OCI". This program often has been mischaracterized as "dual nationality" or "dual citizenship." However, a person who holds an OCI Card in reality is granted an Indian visa, not Indian citizenship. Thus, an American citizen who obtains OCI status remains a citizen only of the United States.

And from the Indian Government's POV:

The Constitution of India does not allow holding Indian citizenship and citizenship of a foreign country simultaneously. Based on the recommendation of the High Level committee on Indian Diaspora, the Government of India decided to grant Overseas Citizenship of India (OCI) commonly known as ‘Dual Citizenship’. Persons of Indian Origin (PIOs) of certain category, as has been specified in the Brochure on overseas citizenship of India who migrated from India and acquired citizenship of a foreign country other than Pakistan and Bangladesh, are eligible for grant of OCI as long as their home countries allow dual citizenship in some form or the other under their local laws.

Technicalities via teh Great Wiki: Indian nationality law

An Overseas Citizen of India will enjoy all rights and privileges available to Non-Resident Indians excluding the right to invest in agriculture and plantation properties. There is no visa requirement for travel to India. The person has to carry his existing foreign passport along with Registration Certificate. Alternatively, the Overseas Citizen of India can apply for a new type of visa called ‘U’ visa which is a multi-purpose, multiple-entry, life-long visa for those that wish to acquire it. It will entitle the Overseas Citizen of India to visit the country at any time for any length of time and for any purpose.

An Overseas Citizen of India will not enjoy the following rights even if resident in India: (i) the right to vote, (ii) the right to hold the offices of President, Vice-President, Judge of Supreme Court and High Court, Member of Lok sabha, Rajya Sabha, Legislative Assembly or Council, (iii) appointment to Public Services (Government Service). Also Overseas Citizens of India are not eligible for an inner line permit, they have to apply for a Protected area permit if they want to visit certain areas in India.

An interesting question is whether a person registered as an Overseas Citizen of India will lose the right of diplomatic protection by their home country while in India. Article 4 of the Hague Convention on Certain Questions relating to the Conflict of Nationality Laws of 1930 provides that "a State may not afford diplomatic protection to one of its nationals against a state whose nationality such person also possesses". The case depends on two things: first, does the Indian government itself recognize Overseas Citizenship of India as a true citizenship and on that basis refuse the right of diplomatic protection by the other country; and second, does the person's home country recognize it and accept India's refusal. Both points are doubtful. India does not give Overseas Citizens an independent travel document but instead puts a visa in the other country's passport. If a person is eligible to have only another country's passport but not any form of Indian travel document, it is hard to avoid the conclusion that the person is a sole citizen of the other country for the purposes of diplomatic protection.