In Mail.app, you can create to-do items from text in your notes or email messages. What's cool is that you can select a portion of the message and insert it into your to-do list. This is great for when you get an invoice in your email that needs paid, or anything that you need to take action on.
How to do it:
1. Open Mail
2. Select a message that has something you want to add to your to-do list. Click and drag to select the part of the text you want to add.
3. Control-Click the text and choose 'NEW TO-DO' You can also simply click the 'TO-DO' button if you have it visible in your toolbar.
4.This will bring up a box that lets you add a Due Date, Alarms, Priority, and choose a Calendar to add it to. When you do this, it will automatically appear in iCal.
Note: If you are using IMAP email servers, to-dos are stored with your email which makes it available on any Mac you use where you have your email setup.
5. Once you've added some items, you can view the list and use it.
To view your To-Do list in Mail.app, you simply click under the 'Reminders' section in your sidebar and you should see your list.
6. To view it in iCal, open iCal and if it's not already showing, choose 'VIEW -> Show To-Dos'.
That's all there is to it!