If you already spend a good chunk of time on Twitter (like I do), why not use it to get organized and manage your to-dos? TwitDo uses Twitter to build your to-do list, so you can add tasks and mark them complete without ever leaving your favorite Twitter app.
TwitDo is incredibly simple to use. Just post a tweet with the hashtag #todo, and TwitDo will automatically add it to a to-do list at a personalized URL that uses your Twitter handle. After you've added a few items, visit your personalized TwitDo page to see how your list is shaping up. When you've completed a task, tweet a keyword from your memo with the hashtag #done to tell the service to mark it as complete.
The service has some drawbacks: first, your to-do items are public when you post them, not @-mentions, meaning everyone sees them. Plus, since the service is completely public and doesn't require a login, anyone can access your to-dos if they notice what you're up to.
While privacy isn't TwitDo's strong suit, simplicity and ease-of-use are. You don't have to sign up for an account, you don't have to configure a to-do list or categories, you just start tweeting as your to-dos come to mind and refresh your to-do list to see them all at once.
Click this link to get started with TwitDo.