When adding a task I often type the description then use the buttons below to assign to a list, add tags, prioritize, pick a due date. Once I start using the buttons it is helpful to hide the keyboard to see more of the list, but once I'm done with tasks I have to bring the keyboard back to press enter.

It would be very helpful to have an enter button, maybe as the last thing on the right to make it easy to submit a task after hiding the keyboard.

I'm posting this in the Android category because that is what I primarily use, but it would probably also apply to the iPhone app.