If you check the At a Location checkbox, you're then prompted to provide details about the location you'd like to use. You can either enter a contact's name (provided that contact has an associated address in Contacts) or street address. Then you choose whether you wish to be reminded when you arrive it or depart from that location.

Any scheduled reminders will appear in Notification Center on your Mac; you can snooze them or close them when they pop up. Snoozing resounds your reminder fifteen minutes later--not just on your Mac, but on any iCloud-synced iOS devices.

Other per-reminder options include recurrence, priority level, and the ability to add a note. Adjusting priorities doesn't change where tasks appear in your list, but it does add an exclamation-point icon to indicate which tasks are more important. You can drag and drop to rearrange tasks, or even drag tasks between lists.

Keyboard navigation fiends, take note: You can type the first couple letters of a task to select it; then Command-I to edit it.

To mark a task a complete, click on its checkbox (or, with the task selected, hit the Space bar). You can view all your completed tasks, across all your lists, by choosing the Completed list in the sidebar. To see per-list completed tasks, scroll up past the first item in the list to reveal its own Completed section.