Not quite on point, but since the issue came up in a previous comment, here's my 5-minute adhoc solution for working with tasks and getting them syncing between iCal on iPhone and iCal on the desktop.

I created an event titled 'Tasks', set its time to be the first event of the day (from 12am to 12:15am), and in its 'Notes' area I created a kind of simple task list template, just set up in a vertical list the basic context headings that fit my weekday routine - 'Home:', 'Office:', and 'Out:'. Beneath each of these context headings I added 4 blank lines headed by a bullet point. Then I set this event to repeat daily on weekdays. My routine changes a bit on weekends, so for Saturdays and Sundays I set up a similar repeating 'Tasks' event but with different contexts. That's it.

Now, I don't claim to be a GTD adherent and I know this is a bit adhoc, but I like this solution for a few reasons.

First, I personally need to associate sets of tasks with a particular day - and this is a simple way to do that. You just tap the day, and there's the day's schedule with the 'Tasks' at the top. Tap 'Tasks' and there are all the tasks laid out neatly and clearly by context on a single scrollable page.

Second, an iCal Event's 'Notes' field allows for a lot of flexibility to organize your lists the way you want, to enter as much or as little information as you want (I'm not in Leopard yet, but I assume this is unchanged). And because the iPhone/iPod Touch makes it super easy (even enjoyable) to edit, the system is an easy one to stick to.

Third, no problems syncing with iCal.

Fourth, you never have to use the iPhone's yellow-lined notes program.

Again, it's adhoc and not particularly original or particularly clever, but until iCal To-Dos sync well with iPhone, I've found this to be a pain-free workaround with pretty good results.