So I'm flying with an infant in my lap. When choosing my seats I chose a window seat with an empty middle seat. There are a few other empty middle seats on the plane so I'm hoping no one takes the one next to me, because we could use the extra space and I won't have to worry about my boy bothering the person in the seat next to us.
Now, I figure that if people who are picking their seats knew that I was travelling with an infant, they would choose to sit in one of the other middle seats - for their own good. But the seat map doesn't tell us that information. So, I think it would be useful if it did. The airline could make this an option for me, to show that to others. I care what other people choose, and so I'd like to communicate information to them that will help with that. The airlines should think about letting passengers do this.
They could even go farther. If someone is single, let them display their age, sex and single status. People could choose to mingle (or not). People may not want to sit near people with kids. There may be more options (photos, show me who on my flight is facebook friends with me, etc...). I think this could be how things are going with social networking and such.