Because you have a calendar set up with all your projects and due dates, and your email all on one screen, you now have everything you need to keep track of what you are doing and what you have done in one place. There's no more keeping track of slips of paper, running multiple programs, trying to remember what you have or have not done or trying to keep track of everything in a variety of different programs .
Keeping track of everything with Google Calendar and Gmail via iGoogle is a wonderful tool, and it is an entirely free way to manage your projects. The image to the left shows you my iGoogle screen with an arrow showing you how to add items to it.