My first serious experience with time value of money came right after college where I received a number of offers to issue me a credit card. Being young and naive, I thought it was a great idea! It felt like "free money" every time I signed a bill and I was also a bit overzealous at last minute, unneeded purchases (impulse buying) when shopping. That was my first "hands on" experience with APR and learning that the interest charges on those purchases were significantly higher than I had expected. There were months when I first started working (just out of college) where I could just pay the minimum payment and those interest charges kept growing and growing. It was a hard lesson to learn!

What have been some of you experiences with stuff like this?