I'm notorious for the amount of email I receive and the difficulties I have keeping up with it. My best estimate is that I receive about 200-300 emails each day.
On those few blessed occasions when I do get my inbox into single or double digits, I feel both enormously productive and focused. (Alas, the feeling doesn't last long)
The problem is that the inbox is most people's default choice for managing their work. It's a matter of convenience. Because email is the medium through which most requests and work assignments arrive, we seldom take the time to transcribe that work into any other medium.
Unfortunately, email is pretty much the worst system you could design for task management. There's no concept of priority--by default, whatever is most recent is granted visual priority. As a result, people who manage their workflow via email tend to focus on what Steven Covey calls Quadrant 1 and 4 activities: urgent and important, urgent and unimportant. This leaves Quadrant 2 activities (important but not urgent) to languish while we spend our time on trivialities.
But for all its flaws, email is here to stay. The floor of the Valley is littered with the bones of would-be "email killers." To have a shot at success, any solution has to work with, rather than try to replace email.
Here's one possible solution, which I offer up to the entrepreneurs of the world, free of charge.
1) When I read an email, give me a single button that lets me mark it as a to-do.
2) When I view my inbox, all to-do emails are displayed at the top of the inbox. Only after all the to-dos are shown do new emails appear.
3) If a to-do isn't urgent, give me one button to bury it--keep it in the inbox, but show it after the other to-dos and unmarked emails.
If you implement this, let me know, so I can become your first user!