Looks like fun, and I'll have a play in a while.

A couple of things from the top of my head; Alfred integration would be cool, currently I keep nothing in my dock (other than finder and trash) and launch everything via Alfred, being able to launch a group by name in Alfred might be cool.

On switching groups, when it's choosing what to close, does it only close app's that are explicitly listed in other groups? How does it cope with tray apps like dropbox? When I (infrequently) fire up Steam/games I tend to manually kill off a few of the background servicey apps like dropbox I'd otherwise leave running all day.