I've been using it with Toodledo. I'd considered a switch switch to Remember the Milk but Toodledo tech support helped me with my major concern -- the ability to apply operations to sets of items. The combined cost of ToDo.app ($10) and Toodledo ($17) together is $27 - a good fraction of MobileMe. Too bad Apple hates us.
Here's what conventional, good, reviewers will tell you about ToDo.app
Macworld | iPhone Central | Review: Todo 1.1.1 for iPhone and iPod touchThis is what you only get from me:
... it’s in creating and organizing tasks that Todo really shines, offering many more features than Zenbe Lists or any of the basic to-do apps I covered a few weeks ago.
As with other apps, you can create multiple lists of tasks; you add new lists and tasks using the plus (+) button at the top of the main lists screen or any individual list screen, respectively. When viewing a list, tapping on a task’s circle marks the task as complete; depending on your settings, completed tasks disappear completely or are moved to a Completed section at the bottom of the current list..... Creating a new task demonstrates Todo’s best attribute: offering many options and features while keeping the interface simple and easy to use. In addition to naming a new task, you can specify a due date, a repeating schedule, and a priority (1, 2, 3, or none); you can also include a text note...
- If you try to switch services, say from ToodleDo to RTM, every item on your list is deleted. So you can't decide to use one service, then switch. [Update: Appigo consciously decided to do this for the initial release, they will probably make this configurable in a future release.]
- Tasks can belong to only one list/category/tag. (Very much like Palm -- in fact ToDo.app is pretty much a functional clone of the original Palm To Do app).
- There are no alerts or alarms on tasks.
- There's no search. I really need search. Of course this is a problem across the entire iPhone. [Update: Appigo expects to deliver search in a near term release]
- It's crashed once in light use.