Today I received a phone call from Citi welcoming me to the new Citi Diamond Preferred Rewards World Mastercard. They stated that my old Dividend card will automatically switch to the new card if I do nothing by June 30, but that I can keep my old card if I want. Others have received the same offer, and I found some good discussion about the topic at Fat Wallet. Many people are rejecting the offer. One of the reasons being that the new card has no credit limit, which can hurt your credit s...