On a personal note, I knew people at the Boston marathon finish line, as I'm sure many of you did as well. My parents had friends in the World Trade Center. If we could stop that in the future, that is worth a small sacrifice in personal liberty. Again, this a personal opinion, one that many do not share.
To me, the key is creating adequate oversight to control this leviathan. We need a real court, with proper appointment procedures and adversarial process. We need restoration of legislative oversight. Most importantly, we need strong encryption on the systems that can only be unlocked with a court order.
In fact, this was the original design of Total Information Awareness. The privacy tech got gutted somewhere in development, but there's no reason we can't bring it back.