How I love gmail! That’s really the best free service I could ever imagine. Even if they read all my emails, I don’t care.:) Gmail saves my time significantly now. Especially when the ‘Tasks’ feature has been added. You can have your TODO just with your gmail web application. Everything under hand, very convenient. So how I use gmail to manage my time:

I create tasks I need to do. Then I order it by from high priority tasks to low priority tasks. The hot keys make it very easy and fast: just use CTRL and arrow up/down keys.
Gmail allows to print the tasks out, search for tasks completed on specified date, etc. I think it is very useful time management solution. If you ever read the ‘Getting Things Done’ book, you’ll understand.
I’m impressed and thankful. Bravo, Google!