A manager's work is different than a technical person. A manager's span of influence is much broader, so managers tend to have more (smaller) tasks, especially tasks that move across the organization. For me, and for my colleague, that requires a different set of organizing skills.
Once you're managing several people, you need a low-level project portfolio. That way you can see what everyone is working on, and resolve any context-switching (so technical people get their work done more quickly). You'll need one-on-ones to check in with folks on a regular basis, so you know if their work is at risk. These two organizing "tools" allow you to see all the work people are doing, so you know if you need to change what you're doing.
Don't think you can manage the management tasks with a project scheduling tool. That's the wrong tool for disparate tasks of varying sizes with no interdependencies except for you. As with any system, first decide how you need to organize and manage the tasks manually, and then you can see if an electronic tool will help.
http://jrothman.com/blog/mpd/2007/11/getting-organized-whats-different-about-managers.html
