The next version of OS X, code-named Leopard, will have the ability to simply mark any text in Mail as a new todo. Something to look forward to since most emails come with multiple actions to take; and treating one email as actionable without separating out those individual actions means that some of those actions may never get reviewed or done on time. As Merlin notes in the latest podcast discussion with David Allen (http://www.43folders.com/2006/11/28/productive-talk-comp/), it is best to get emails out of the Mail program in order to do something with them.

MailTags works well for this. So that's one way to go. My own approach is to use the great "select text" - "option-key" - drag feature of OS X on the Mac. Any time I find actionable content or tasks in an email, I simply select the text, and option-drag it to a folder on my desktop called "Inbox." Doing this makes a clipping of each selection of text that can then be viewed, printed, or manipulated however I wish. I use this functionality with Ready-Set-Do! (http://homepage.mac.com/toddvasquez/apps) which allows me to process these clippings by specifying next actions for them and filing them in other folders on the desktop (e.g. Inbox, Actionable, Projects, Waiting For, Read-Review, Tickler, Reference, Send to PDA, Send to Paper). Of course, I prefer this approach because I also designed it.

But if you're already used to Entourage or Outlook you can look into that functionality on the Mac as well. There is a GTD Outlook Plug-In available but I believe it is only available for the PC, not the mac. But there are lots of alternative programs on the mac for getting things done; and with Apple's new OS X to debut sometime next year, making tasks out of emails and any other program will be built right into the operating system itself.