This is a little edit: I just want to say that also in the book mentioned below, you'll see that no, you have not ruined your baby's mind. Babies and children have this fantastic plasticity in their brains that can change the way their brain works. But also, you'll see that a lot of things get wired in there from ages 0-3 that are semi-permanent. The Science of Parenting is another good book on this.
I know you've gotten lots of answers, but I have a lot of passion about this. I recently read a book called "Bright From the Start" by Dr. Jill Stamm. She explains what is happening neurologically in babies brain development. She talks about what happens when a baby watches TV, and it is VERY BAD. What we need to understand first off, is that a baby's brain DOES NOT process what they see on TV the same way an adult does. Babies are mapping everything they see into their brain. The second thing is that babies don't know anything about how the world is made up, and they are making connections at a rate that is incomprehensible rate to adults (because we have already made all those connections). They need all their senses to integrate, and everything to be in a 360 degree, 3 dimensional context to correctly map how the world works and is put together. A TV image has no smell, temperature, depth, texture, and it has nothing to do with the room it is in. When a baby watches it, the baby incorrectly processes what he/she is seeing, as real. That is why babies who watch TV can have sensory integration disorders later, and that is why yes, I'm sorry, but 10 minutes is too much. The AAP is serious when they say NO TV for children under 2, and VERY limited after that.
Babies are seeking things to learn, and they are fascinated by many many things, especially things that have different textures and patterns. This is because they are figuring out that when something looks like this, it feels like this, etc. Dr. Stamm uses as an example, to remember when you were learning to drive. Remember how heightened your awareness was of every little thing? Noises, spatial sense, motor skills, etc? Babies brains are firing away even faster, all the time they are awake. And then as they learn, things slow down, just like now you drive without thinking about it all that much.
My son never saw the TV until he was 2.5 (and then it was just the news on TV for us, not a kids show), and didn't see a kids DVD until he was 3. He is able to amuse himself basically indefinetely during the day. We interact with him, of course, but he just plays with his trains, a ball, or animals or whatever. He's extremely easy.
I'm glad you're aware and looking to do the best thing for your baby. I highly recommend the book I mentioned. She has easy little games to play with your baby to give them optimum development. It's a great and fascinating book.
I also want to point out that there was a massive recall of Baby Einstein DVD's last year, under pressure of a lawsuit of deceptive business practices. Disney offered people their money back if you brought in your DVDs. The reasons were because it is well known in the medical and scientific community that it is bad for babies development to watch TV, not good for it, as the DVDs claimed. I'm sorry for the people who were decieved by the ad campaigns and false advertising, but it is not a benign thing to let a baby watch TV.
Also, it is the TV that triggers ADD. That's because babies are learning to develop sustained attention, but TV switches views every few seconds, and that disrupts attention. There is a positive link between young children watching TV and ADD/ADHD at age 7, and also for sensory integration disorders. There is even a Cornell University study that found a positive correlation between higher autism rates in young children who were TV watchers.
If you are over 30, you probably did not watch TV as a baby. That is why half of our classmates didn't have these disorders in our elementary schools. Now that Disney and others have been marketing to young children for 20 years, we have much worse issues in the schools now.