The iPad can be a great tool for your dad's mobile productivity, if he has the right apps installed.
Documents to Go ($9.99) - Microsoft hasn't yet developed a Microsoft Office app for the iPad, and Microsoft Office Web Apps functionality is glitchy at best from the iPad browser. But, with you can create, view, and edit Microsoft Office files from the iPad. It also acts as a handy viewer for other file types, and lets you add file attachments to e-mail on the iPad.
Remember The Milk (Free) - Dads have a habit of forgetting things. With , dad's to-do list (or "honey-do" list as the case may be) can be kept in order and prioritized to keep dad on task. The items from the RememberTheMilk.com Website can be synced with the iPad app, and e-mail reminders can be set up to give dad a little nudge.