Brightkite and Shizzow have demonstrated that people are willing to transmit their location electronically to at least their friends, sometimes more, in exchange for being open to ad-hoc meetups .
What the leading services to date have focused on is where you are. This is not that useful because it says nothing about how long you'll be there. Whats more useful is where you will be.
To facilitate meetups, I want to see someone's location schedule for the day. That way I can plan my transportation and timing to align, like a Mars vehicle adjusting its trajectory to enter the atmosphere at just the right time.
Many people live by a very predictable schedule. Even for a cafe-person like me, I know my basic schedule for that day. I would be happy to enter that schedule in the morning.
Schedule for Don Park:
|12pm-12:15pm||Food cart on NW 3rd||Yes|
|12:15pm-1:00pm||Waterfront picnic lunch||Yes|
Once the schedule data is in, higher-order correlations can be mined. "When is a good time today to meet up with Bob Smith?" "There is a 30 minute overlap during lunch where you will be 0.5 miles from Bob at a time when he is interruptible". Another example is an automatic alert, such as a gathering of 3 or more friends at the same place. "Four friends are scheduled to be at the Green Dragon starting at 4pm"
If I wanted to meet Bob Smith, why not just call him up and schedule something? These meetups are less official than that. The use case is I have to work somewhere and I want to select the cafe that already has the greatest number of friends/coworkers scheduled to be there for these hours.
Instigating these meetups is difficult when you're the first one. The way to announce your intention is to state a time and place but what if you're only interested in that meeting and its existence depends on another agreeing to the same thing. Thats more like group scheduling and needs more thought.
I was focused on adding a schedule to a location service when I realized that calagator or upcoming are already what I'm describing. They understand schedules and locations. The table above could be put into calagator though it has no notion of a person. Upcoming could handle it. Events in upcoming can be made for friends-only. I would be doing this today but upcoming users are not expecting personal schedules like that. It would end up being spamy.
An open-source project like calagator could be extended or forked to understand the concept of user (which was explicitly avoided to date), and add the 'interruptible' or 'available for meetups' concept to the event.
There is still value to instantaneous location pulled from a GPS or the unique ID of a near-by wifi access point or cell tower. It adds or removes confidence to the schedule since it can say the person has been late/ontime for events recently past.