Sync iOS5 reminders between people using iCloud
The other user (@Paul) is incorrect! Create a list that you want to share using your iCloud account. On your Mac, click "Reminders" to the side of the calendar view in iCal. Right-click on the calendar you want to share, then click "Share Reminder List..." On the menu that appears, select "Only the people you invite" and click Ok.

Easy and effective!