Doit's regrouping feature is very fast and useful. I very often regroup my lists, especially the Next list, many times every day by Project, by Context, by Deadline depending on what I want to do (and I find the sub-sorting by priority within each group to be immensely useful).

I wish there were direct one-click buttons for regrouping, though, because I regroup so often that it becomes annoying to have to open a regrouping menu every time. There is a lot of empty space in the app, for example in the blue area on top or where the quick entry bar is located, or in the new bar at the bottom. There is ample space in any of those places for having a bunch of "group by" buttons. The buttons could be quite small, if you like. For example, you could use the quick entry characters # ! ^ @ & etc to represent the different "group by" modes. The buttons could all sit adjacently to each other as a suite and would not need to take up more than an inch or two all in all, depending on what size and spacing you prefer.

(If you absolutely want to save screen space you could instead take away the quick entry field, and make it a user preference setting to show it, because I for one never use it at all. I always use the "N" key and enter everything by confidently selecting the right projects and contexts etc in the "form" instead of having to spell everything correctly in the quick entry field.)