I haven't gotten very far, but Keith made a comment that stopped me cold:
In the information age, success is less about efficiency than effectiveness—that is, the ability to get the right things done, rather than just the ability to do the things right. (page 18)This explains so much.
There's been a distinctive trend in the "efficiency" and "productivity" books to determine not only how to spend your time more wisely, but also what that time should be spent on. I've read many of them and even blogged about a few, and I know from personal experience how challenging it is to choose the next "right" thing to do, but I have to admit I never connected the dots.
Given all the apps that help us be more productive and how connected we all are, it really is less about efficiency. Yes, building efficient and scalable systems still has merit and is still needed, but you have to first choose which systems to spend those valuable resources on. In other words, before you can streamline something, be sure that you should be spending your time on it to begin with!
So for those of us with too much to do, before you try to muddle through and/or use every productivity app you know of, stop and evaluate your choices first. I'd start by listing out—whether literally or figuratively, whichever you prefer—all the possible tasks and projects you could spend your time on, then determine which one is right for you next, given your priorities of the moment. Then and only then determine the most efficient way to tackle that task or project.
If you work for someone else, you may not have full autonomy on what is "right" for you or not. But you know (or should ask) what is most important for your boss and team and then be most efficient about that top priority.
To summarize, determine what is right (aka, effective) first and then how to do it better (aka, more efficiently).
So what would make you the most effective now?