I don't really get the TODO list thing (even though I think PG mentioned it himself). Is that because people tend to mail their TODOs to themselves? Or because most email translates to TODOs?
I know that I certainly don't want a system that allows people to push TODOs at me.
This is true regardless of your work or workflow. Consider that at the very least most emails tend to be an implicit request for a reply. In most cases that reply requires at the very least remembering some bit of information (in the best case scenario something that is trivially easy to recall). And even more fundamental than that, each email message is an implicit command to digest the information contained in it. But beyond that, it's quite typical for work to be tracked or requested through email, for some jobs it's by far the normal way that the vast majority of work is organized.
Most emails are spam, actually. Some legitimate, but the majority doesn't warrant a reply (like all the "marvel at the new features of our startup" mails). Of course the mix varies from person to person. And they are TODOs in the sense that you feel like you should delete them, or archive them, or whatnot.
I think it would be better to make most of them go away automatically, though. Perhaps things like "automatically save attachments from x into project folder z" would help (already doable? I don't use filters much).
Maybe it really would be better to make emails a universal transport layer and integrate it better with other stuff. People send you a TODO -> goes into TODO list. People send you an image -> goes into photo library. And so on... Of course I always hated the idea of Outlook of allowing other people to mess with my calendar, so I don't know...
I know that I certainly don't want a system that allows people to push TODOs at me.