Thought for the day: the iPod is now usable as a contact list manager as well as an MP3 player. My suggestion for the next step: make it an outline browser. You could create arbitrary outlines in something like OmniOutliner or Radio and carry them around with you on the iPod. The user interface is superb for that.
Some outlining programs have a handy to-do list option. Each node has a checkbox, and an item is automatically checked when all its sub-items are checked. While entering text on the move would be a pain, checking and unchecking things is something you could reasonably do on an iPod.
Checkboxes would probably require changes to the iPod software itself, but simple browsing could be done initially by creating fake MP3 tracks in an appropriate directory hierarchy. That’s how the contact list idea started. Should be easy.
In fact, if somebody gives me an iPod, I’ll implement it…