Oh good, sounds like you know what you're doing! Hopefully you keep making small payments, e.g. $5 monthly fees on each card. If you leave a card unused for a long time that can lead to some nastiness and a sudden drop in your credit score later. The reason is basically that accounts with much higher credit lines than they actually use are high risk because they have a small chance of a major default.

Source: I used to work in a credit cards division at a major bank.