I've read the book. Basically, the features I have are the minimum I needed where I first rolled out the system (my day job). We had to have something that lets people share tasks, and keep track of time. Like they also say in the book, I realize those features aren't for everyone, so I'm happy to concentrate on the niche of people who need them. At work, they really like the system, so I'm confident they're out there.
Also, some extras that Stuff To Do has:
* Groups - share tasks with other people in your work group with simple drag/drop.
* Time tracking. Keep track of how much time you've spent on each thing.
* Reports. No fancy graphs, yet, but it does break things down by day and task over preselected time periods.