Friends note that OCI's may NOT be completely exempt from Registration contrary to what has been said in the media and consular websites. See
http://www.manupatra.com/asp/newsletter 119.asp for the actual Notification in the Gazette of India. Scroll down to Ministry of Home Affairs, then to the second notification titled "Registration of Foreigners (Exemption) Amendment Order, 2005". Note it uses the phrase "except rules 5, 9 and 15". Anyone know what rules 5, 9 and 15 are?
Also note the first notification under sub para (b) only exempts Registration with the Registration department, leading me to believe that Rules 5, 9 and 15 may require filling up the special Foreigner "Form C" when staying in a hotel or informing authorities when changing addresses, etc., but I cannot be sure till I see the actual Rules. If anyone can post them as a reply, that will be great.