I have complained frequently about the iPhone's lack of TODO support. I do not buy into all aspects of the Gettings Things Done philosophy (finding it a bit cultlike), but find most of its ideas useful and lightweight. Maintaining a queue of tasks is central to the method, and the iPhone has no support whatsoever for todo lists. Since switching from my Pilot, I've tried keeping lists in google notebook, wikis, and even (a terrible habit, I know) my email inbox. Nothing has quite worked and it looks like Apple has no interest in remedying the situation.
The GTD tool Remember the Milk has now released an iPhone app which syncs to the online version. This gives me more-or-less everything I need to take control of my life again: tasks, priorities, categories, and a syncable desktop. I particularly like the broad interoperation between RTM and other services. Rather than existing in its own isolated stack, I can create and view tasks from RSS, twitter, jott (voice command!), and plain old email. Cool.
My only quibble is with the user interface.( Collapse ) UI quirks aside, this has the possibility to bring my iPhone to near-parity with my 1997 Pilot. Let's hope this partnership works out.