Has anybody quantified the efficiency gains from using emacs to do work rather than conventional means? Are there certain areas (e.g. Mail, todo, notes,calendar,scheduling) that gains more efficiency than others?
I don't think it would be easy to quantify the gains from Emacs because it's too specific to the user. For me, it's all about automation. If I notice myself doing something that can be automated multiple times, I write a function. If I find myself calling that function frequently, I turn it into a keyboard shortcut. That's a huge win, because it eliminates a lot of work I hate to do, but it's very specific to the user.
Gains and losses, remember. There are tasks where the use of a visual IDE just makes things easier to comprehend and use. Emacs will not give an increase in efficiency across the board for all tasks, otherwise we'd all have switched to it long ago!
Perhaps the real benefits are having some fun and warding off Alzheimer's, as the time spent learning and tweaking probably cancels out with future productivity gains.