1. No More Surprises - if they are going to increase your rate, change some of the fees they charge you or make other significant changes to your agreement they have to give you 45 day notice. Therefore you would have the option to cancel the card. However...if you choose to cancel the card they can stick it to you by requiring you to pay off the balance sooner or increase the minimum payment.
2. If you use a credit card, be ready to pay more - now, some merchants can charge you more if you decide to pay them with a credit card. The way they can do this is by requiring a minimum purchase amount if paying with credit card. So if you are one of the many that barely carries cash around, you might have to buy more crap at a store in order to meet the minimum purchase price.
3. If you don't use the card you can loose it - If you have a credit card that you don't use the issuer can try to close the account. Which is not a big deal to begin with if you were not using it. The only down side could be that if you have had the card for a long time, and you close it, it might affect your credit score. I know it's asinine but that is one of the criteria that papa FICO uses to calculates your credit score.