Right now you must have a Dropbox account to use Todo.txt Touch, and your Android device must be online to add or update tasks. (We're working on offline access now, and eventually other cloud sources.)
There are already a multitude of decent task managers for Android, but Todo.txt Touch is a minimalist, plain-text focused solution we built to learn by collaborating on Android development.
Interested in joining in? Fork the project and talk to us on the Todo.txt mailing list.