Pat Dryburgh writes about productivity on the Mac and the iPhone/iPod Touch:
This is where the system begins to fall apart when the iPod touch or iPhone are introduced. While Leopard’s Mail.app utilizes the message URL handlers, Mail.app for iPhone does not. This means that if I am checking my email on my iPod touch and I read one that requires further attention, I need to close Mail, open Things, write down an action that explains in enough detail what the email was referencing, then go back to Mail to continue checking my emails. The other option is less taxing, which is to simply ignore the email on my iPod and address it later when I am on my Mac. However, to me, having to address a dozen or so emails more than once feels very unproductive, and defeats the entire purpose of keeping a clean inbox.