Free idea: a little gizmo like a pager that you could wear on you that notifies you of the return code of the last command you ran. Just imagine running a compilation job, leaving the room to do some chores, and then after a few minutes getting a pinged with anything that's not a 0 because the compilation didn't run correctly; you'd get to fix it immediately instead of getting the unpleasant surprise hours later when you come back, saving you precious time.