Keep an eye out for unwarranted cancellations. Credit cards issuers are trying to lower risk by canceling credit lines that have gone unused for certain extended lengths of time. The story over at Consumerist mentions Citibank by name, but others may be doing this as well.
http://consumerist.com/5059536/your-inactive-credit-cards-could-be-in-danger
UPDATE: It seems that Bank of America is also doing this to account holders.