OmniFocus can alert you to nearby, "as long as you're there" errands.

Computers have never been a threat to the popularity of the pad-and-pencil method of organizing your life. When a thought strikes, immediate access is more important than computing power. But the $19.99 OmniFocus for iPhone gives both.

Like OmniFocus for Mac OS X, the iPhone version forces you to stick to methods in David Allen’s book "Getting Things Done" (GTD). "Actions" (such as "Buy milk") are matched with a single "context" ("Supermarket"). Want to assign multiple contexts or a priority rating to an action? Tough--that's not The GTD Way, so OmniFocus doesn't permit it. GTD supporters say that this inflexibility keeps the system simple.

GTD encourages you to write down tasks as you think of them, which suits the carry-it-everywhere iPhone well. Just as importantly, OmniFocus for iPhone is well-matched to the optional $79.95 Mac version. It supports wireless syncing between the two using Bonjour, WebDAV, or MobileMe. We mostly relied on Bonjour, making an easy connection.

But while OmniFocus for Mac and iPhone play together nicely, some handy, expected features from the Mac version were missing on the iPhone. For example, OmniFocus syncs with iCal on the Mac, which shows OmniFocus items as To Do items; there's no such integration with iPhone's Calendar. We didn't mind the loss of some other Mac app features, such as the Perspectives task-organization system, especially when they were replaced by simpler, iPhone-like substitutes (in this case, "Smart Groups").

On the plus side, the iPhone version lets you illustrate an action with the device's built-in camera, or leave voice notes via the microphone. Finally, OmniFocus uses the iPhone's location-sensing abilities to help you group errands. In other words, it reminds you that the library's right near the bakery, so why not do both tasks at once?