Google's Gmail team moved to plug this hole with a new task manager that lets users keep track of their agenda. Check out this task management list example here, then begin creating your own tasks by activating the feature in Gmail Labs.
Go to Settings atop your in-box, click the Labs tab, and you'll see the new feature option at the top. Select Enable and click Save Changes at the bottom. You should then see the Tasks link under the "Contacts" link on the left of your in-box.
Click it, then click in an empty part of the list window that pops up on the right and start typing your task list in what is really the familiar Google Chat window. This means they're visible while you're scanning your in-box, reading mail or searching. You can also pop your list out into a new window.
The list you create saves automatically, and you can hit Return to begin entering a new task. There are a number of editing options, including the ability to add, delete, indent, un-indent tasks, move tasks up or down, or switch between task lists.
Here's the best part: You can also convert e-mails into tasks. To do so, select one or more messages and go to "More Actions," then "Add to Tasks." It pops up in the task list. You can read it by selecting it and clicking the related e-mail link. Awesome! More modular e-mail. It's like putting a digital sticky label on your to-do list.
ReadWriteWeb's Marshall Kirkpatrick does what the Gmail team failed to do: create a video demo of the task tool here.
Very cool, though like TechCrunch's Erik Schonfeld, I'm not much of a list guy. For work, I send a daily news budget to editors and that's it. For play, I keep a mental list each day. I'll have to play around with it some more to see if my opinion on to-do lists changes.