I was one of those who always grabbed a Diet Coke or Diet Pepsi when I was thirsty. Used to be once a day, then twice, then all the time. I was hardly drinking water or milk. I kept reading how bad it was for me, but had no intention of giving it up. Afterall, it was diet so there was no sugar, no calories and the dentist always raved about how good my teeth were.
Then a couple of months ago I noticed the bottom of my two front teeth looked like they had something black on them. Like a thin black line at the bottom of my two front teeth. Upon closer inspection in the mirror, my teeth weren't black, they were see through! I went to my dentist and he said it was acid erosion most likely from the soda. It was wearing the enamel off of my front teeth and would get worse if I continued drinking soda. So, I had to cut way way back -- like to 2 sodas a week! At first I thought I could switch to a diet ice tea or sugar free lemonade, but all of those drinks have the acid in them, too! It's amazing how many foods have acid, but soda and lemons are some of the worst. So no more water with lemons, no lemonade, no sodas for me.

I have my bottle of water sitting right next to me now and am trying so hard to just get used to it.
For those who think they can keep drinking several sodas a day and not worry -- I was the same way. Now my teeth are messed up -- and my smile was always something I took pride in. I'm thinking about getting composite restorations, but right now it's not in the budget. One thing I do make sure to do when I do get my twice a week sodas is to drink the soda through a straw -- never from a can or from a bottle because it just washes right over those front teeth.
Another thing I learned is to not brush your teeth for an hour after drinking soda or foods with acid in them because the acid weakens the tooth enamel and then the brushing takes that loose enamel away. Wait at least an hour before brushing after drinking/eating acidic foods & drinks.