Just trust me when I say that once you remove the ball and chain of capped internet, you WILL start using more. I felt exactly the same way, "6GB is enough for me, I'm careful and I seldom hit my cap". Now I use 300GB a month at least and I doubt I could go back to using less.
You'll click HD on every youtube video, start downloading a few big games off Steam, download those big applications or linux distributions you've been wanting to try, let your windows and games automatically update, stream full movies off the internet, try out a few of those big MMOs that you just didn't have the cap to download before (and update them with the typical 300mb-2GB MMO patch), host a couple LANs where your friends can come over and use your internet and they can all do the same without you ever having to worry about it.